Labour did nothing wrong when party officials campaigned for Kamala Harris in the US election, a former Conservative minister has argued, after Downing Street faced fury from Donald Trump about the move.

Robert Buckland, who has also campaigned for Harris due to his distaste for Trump, said it appeared that Labour activists who knocked on doors had volunteered and covered their own expenses, which would not be a breach of US laws on overseas involvement in elections.

Trump’s campaign filed a legal complaint alleging that apparent efforts by Labour’s head of operations to organise volunteers amounted to “illegal foreign national contributions”, and hit out at what it called Keir Starmer’s “far-left” party.

After Starmer said he believed the row would not affect his relationship with Trump, Labour officials insisted that the party had no role in organising or funding staff who joined US campaigning efforts, and that such volunteering was by no means unusual.

The Trump legal letter, sent to the US Federal Election Commission in Washington, also complained about what it called “strategic meetings” at August’s Democratic national convention in Chicago between Harris’s team and Morgan McSweeney, now the prime minister’s chief of staff, and Matthew Doyle, Starmer’s communications director.

Labour officials said that the pair were at the event only as observers. The party paid for McSweeney to attend, and Doyle’s costs were covered by the Progressive Policy Institute thinktank.

Buckland, a former justice secretary, who stepped down as an MP at the general election, said a since deleted LinkedIn post by Labour’s head of operations offering to arrange housing for 100 current and former party officials campaigning for the Democrats in swing states was “unfortunate”.

However, he told the Guardian he did not see any sign of wrongdoing. “It doesn’t look like it to me,” he said. “If these individuals are going under their own steam, paying for their own flights and doing their own thing, and their accommodation is either they’re staying with friends or they’re paying for it, there’s not a problem. But they’ve played into the Trump-Vance campaign hands, and that press release was the sort of politicking that you’re going to see this close to an election.”

Starmer, speaking to reporters travelling with him to the Commonwealth summit in Samoa, said such volunteering had happened at “pretty much every [US] election”. He said: “They’re doing it in their spare time, they’re doing it as volunteers, they’re staying I think with other volunteers over there.”

Asked if it risked jeopardising his relationship with Trump if he becomes president again, Starmer said: “No. I spent time in New York with President Trump, had dinner with him, and my purpose in doing that was to make sure that between the two of us we established a good relationship, which we did.”

There was some muted criticism of the government from the Conservatives, although Oliver Dowden, the party’s deputy leader, did not raise it with Angela Rayner when she filled in for the absent Starmer at prime minister’s questions.

John Lamont, the shadow Scotland secretary, told BBC Radio 4 that Labour had created a “diplomatic car crash” that risked undermining relations with Trump.

Nigel Farage, the Reform UK leader, told GB News that the LinkedIn post seemed to show a “very clear breach of American electoral law” and he did not believe the Labour staffers had covered their own costs.

Farage attended the Republican national convention in Milwaukee in July. His entry in the MPs’ register of interests says the near £33,000 costs for him and a staffer were paid for by a Thai-based British businessman, Christopher Harborne. Farage listed the purpose of the trip as “to support a friend who was almost killed and to represent Clacton [his constituency] on the world stage”.

The former prime minister Liz Truss also attended the event, although by then she was no longer an MP.

One Labour MP, Ruth Cadbury, used a holiday in September to campaign for Harris in New Hampshire, while no sitting Conservatives are known to have volunteered in the same way. Almost none have publicly endorsed Trump.

Buckland said this did not surprise him, calling Trump “not a Republican”. He said: “I think most Conservatives would identify themselves with Ronald Reagan and Dwight Eisenhower and George HW Bush, and even George W Bush, not this character.”

Rachel Reeves will announce at the International Monetary Fund a plan to change Britain’s debt rules that will open the door for the government to spend up to £50bn extra on infrastructure projects.

After weeks of speculation, the chancellor will confirm at the fund’s annual meetings in Washington on Thursday that next week’s budget will include a new method for assessing the UK’s debt position – a move that will permit the Treasury to borrow more for long-term capital investment.

The change to the debt rule will be welcomed by the IMF, which says spending on UK infrastructure projects should be ringfenced as the government seeks to repair the damage to the public finances caused by the pandemic and the cost of living crisis.

Reeves will not specify while in Washington which of the various debt measures under consideration has been chosen, but the Guardian has been told by a senior government source that she will target public sector net financial liabilities (PSNFL).

This yardstick – which will replace public sector net debt – will take into account all the government’s financial assets and liabilities, including student loans and equity stakes in private companies, as well as funded pension schemes. This would give the chancellor room to increase borrowing for investment in long-term infrastructure

Labour inherited a set of fiscal rules from Reeves’s predecessor, Jeremy Hunt, dictating that day-to-day spending be met by revenues and that debt as a share of the economy must be falling in the fifth year of forecasts produced by the Office for Budget Responsibility.

Hunt was only narrowly on course to meet his debt rule, by £8.9bn, after announcing large tax cuts despite spending pressures linked to Britain’s high debt servicing costs, ballooning demand on public services and weak economic growth.

Had Hunt adopted a PSNFL target in March, it would have added about £53bn to his borrowing headroom.

The Treasury has hinted that it would not initially take advantage of all the extra scope that a change to the debt rule would provide and would put “guard rails” in place to ensure investment projects deliver value for money. Sources said energy and transport projects would be a particular focus of capital spending in the budget.

Reeves will not go for the most radical rule change by adopting the public sector net worth (PSNW) measure, which also includes non-financial assets such as the road network, schools and hospitals, sources said.

The chancellor will say in the budget that the government’s main fiscal rule will be that day-to-day spending should be covered by tax receipts, with borrowing used only for capital spending. The Treasury says this will mean tax increases and spending cuts of up to £50bn.

Announcing the changes at the IMF will signal that the chancellor is keeping a traditionally conservative body on board with her plans, while aiming to win over the world’s most powerful finance ministers and central bankers.

The push to minimise any reaction in financial markets from a change in the fiscal rules stands in stark contrast to the approach of Liz Truss, who was directly challenged by the fund over her mini-budget in 2022.

A government source said that, while in Washington, the chancellor would explain why she thought a change to the debt rule was needed but that full details would be provided in the budget.

Speaking at a press conference to mark the latest release of the IMF’s Fiscal Monitor publication, Vítor Gaspar, director of its fiscal affairs department, said: “As in many other advanced economies, public investment [in the UK] as a percentage of GDP has been trending down.

“Challenges associated with the energy transition, new technologies, technological innovation and much else mean public investment is badly needed.

“The Fiscal Monitor emphasises that public investment should be protected in budgetary procedures that foster sound macroeconomic performance. The fact that that issue is very much at the centre of the debate in the UK right now is very much welcome.”

The IMF has steadily shifted its stance in recent years to favour government borrowing for investment in the right circumstances.

Requirements for gardens and the planting of trees must be included in Labour’s planned new rules for housebuilders, green groups have said.

The government is drawing up its future homes standard for new developments and it is not yet clear what requirements there will be for green space.

Developers are currently subject to biodiversity net gain rules that mean they have to ensure there are more spaces for nature after a development is built than before construction commenced.

Gardening groups including the Royal Horticultural Society (RHS) are now asking for rights to green spaces to be enshrined in the plans to boost housebuilding. Prof Alistair Griffiths, the RHS director of science, pointed to a study based on UK Biobank data that showed people with gardens tend to have lower mortality risks, lead healthier lives and be less stressed.

“If you have more green space or a garden, you will do more physical exercise and be more likely to meet NHS guidelines for physical exercise. One of the greatest challenges the government faces in terms of the health service is levels of obesity, so this is significant,” he said.

Clare Matterson, the RHS director general, said that including gardens with the 1.5m homes that the government has pledged to build could save the NHS money.

“Let’s completely flip back around and make sure the outside space is actually thought about as much as the inside space. It has so many benefits, cost-saving benefits, particularly to the NHS,” she said.

She added that homes on the market should have a garden performance certificate, like they have for insulation, to indicate the quality of the soil, the amount of water it stores, and the biodiversity.

“When you buy a house you get an energy performance certificate, you have ratings for all the white goods in the kitchen. How about having a garden performance certificate?

“Let’s allow people to make some really important choices and give an incentive for people who are selling homes to create really good gardens.”

Developers often plan to include gardens and green space but overspend on the construction of the homes and put concrete where plants should be. Wayne Grills, the chief executive of the British Association of Landscape Industries, urged Labour to include gardens in its plans.

“We can actually be in there advising the contractors that are there at the same time that construction is going on, rather than being allowed to come back and dig up that same piece of environment,” he said.

“And the second thing for me [is] making sure that the budget is there. So we certainly see some really good, specified schemes, but very often the building is overspent over time and then landscaping that goes around it is cut back in many cases.”

Griffiths said that in the medium-term future, the UK would have a climate much like that of Barcelona now, and would need more planting.

“If you look at car parks and if you look at housing estates and developments in this country, there are no trees and there is no shade. This is not the case in France, Barcelona [north-eastern Spain] and other countries, they have spaces designed for urban cooling,” he said.

A spokesperson for the Ministry of Housing, Communities and Local Government said: “The government recognises the importance of building high-quality housing, and our planning reforms set clear expectations to ensure new developments meet the standards required.

“This includes taking into account the national model design code, which makes clear that open spaces, including private outdoor spaces, contribute to the quality of a place and to people’s quality of life.”

Labour peer Lord Waheed Alli committed four minor breaches in his register of interests, a report has found.

The breaches are not related to previous revelations that Lord Alli paid for clothes for senior Labour figures, including Sir Keir Starmer, and allowed some of them to use his properties.

A House of Lords standards commissioner recommended Lord Alli apologise for failing to properly register his interests in a series of businesses and a charitable foundation.

In his apology letter to the Chair of the House of Lords Conduct Committee, the peer accepted the findings and vowed to “endeavour to follow the Code of Conduct at all times to prevent this from happening again”.

A complaint triggered an investigation into Labour donor Lord Alli, who was already facing scrutiny over his donations of clothes to senior politicians.

A report by the House of Lords Standards Commissioner found that Lord Alli improperly removed his controlling stake in Silvergate BP Bidco Limited, the media company behind CBeebies show Peter Rabbit, from the register.

Lord Alli sold part of the company to a Hollywood studio in 2019 and no longer benefited financially from his shares, but still maintained a controlling stake in the firm.

The commissioner found Lord Alli also failed to register that he was an unremunerated director of a firm in the British Virgin Islands tax-haven in time.

Lord Alli correctly registered his trusteeship of The Charlie Parsons Foundation but should also have included his position as an unremunerated director of the foundation, the commissioner found.

Lord Alli co-founded the charity, which focuses on investing in “new talent, new projects, and new business ideas” in the TV and entertainment industry.

In the report, the commissioner said: “While I consider each individual breach of the Code to be minor, I have found there to be four breaches in total, and have therefore recommended that Lord Alli write a letter of apology.”

In his letter to Conduct Committee chair Baroness Manningham-Buller, Lord Alli said: “I am writing to you today to offer my apology for my breach of conduct by not registering my interests correctly.

“I will endeavour to keep to the Code of Conduct at all times to avoid such circumstances again.”

Keir Starmer has insisted he wants to “look forward” rather than have “very long endless discussions about reparations on the past” in his first comments on the issue before the Commonwealth summit.

The prime minister is under pressure to discuss reparatory justice with Commonwealth countries, most of which are former UK colonies, in Samoa this week.

Speaking to reporters travelling with him for the summit, Starmer said Commonwealth countries were “facing real challenges on things like climate in the here and now”.

“That’s where I’m going to put my focus, rather than what will end up being very, very long, endless discussions about reparations on the past,” he said. “This is about stance, really, looking forward rather than looking backwards.

“Slavery is abhorrent … there’s no question about that. But I think from my point of view and taking the approach I’ve just taken, I’d rather roll up my sleeves and work with them on the current future-facing challenges than spend a lot of time on the past.”

Caricom, a group of 15 Caribbean countries, has indicated it will push Starmer and the foreign secretary, David Lammy, on the issue at the Commonwealth heads of government meeting (Chogm) in Samoa.

In 2018 Lammy, then a backbench Labour MP, called for reparations to be paid to Caribbean nations. But in government Labour has ruled out apologising over Britain’s role in transatlantic slavery.

Starmer said the focus of the summit should be “growth and trade” between Commonwealth countries.

Starmer’s comments on reparations prompted criticism from historians and campaigners who said they showed a lack of leadership and a fundamental misunderstanding about what leaders in the global south had been calling for.

Eric Phillips, the chair of the Guyana Reparations Committee, said: “I just don’t understand the relevance of the Commonwealth if PM Starmer takes this cruel approach.”

He argued it had been slavery that underpinned, nurtured and rewarded “the rampant capitalism that has today created the climate change crisis”, adding: “Britain … wants to trade with Commonwealth countries now that Brexit has hurt its economy. The trading principles are purely capitalistic and against the interest of former colonies. No reparations, no trade should be the new motto of countries that seek reparations.”

Liliane Umubyeyi, the director of African Futures Lab, said: “Heads of states like the prime minister of Barbados, Mia Mottley, have been saying that the demands for reparations don’t concern only what happened in the past, they concern contemporary conditions of inequality.”

Prof Verene A Shepherd, of the UN committee on the elimination of racial discrimination and director of the Centre for Reparation Research at the University of the West Indies, described Starmer’s remarks as dismissive. She said they “will not make the campaign go away, and I hope that those who continue to be affected by the legacies of British colonialism will tell him so when they see him at the Commonwealth heads of government meeting”.

The veteran Labour MP Diane Abbott said: “It is disappointing that the PM has been so dismissive of the opportunity to debate reparations … The descendants of slaves live with the consequences of the transatlantic slave trade in the here and now.”