Boris Johnson has been told by a number of Tory former ministers and serving MPs that he risks jeopardising Britain’s leadership at the G7 and the Cop26 climate summit this year if he goes ahead with plans to cut UK aid by a third over two years. Sir David Lidington, who was Theresa May’s de facto deputy prime minister, will tell an Institute for Government conference on the G7 on Tuesday: “Sadly, the proposal to drop the UK’s commitment to 0.7% [of gross national income] will make it harder to achieve the prime minister’s ambitious objectives for both the G7 and the climate summit.” Anthony Mangnall, who was adviser to William Hague at the Foreign Office and now an MP in the new intake, joined the warning about the impact on the UK’s leadership status, saying: “The UK is the only G7 country cutting aid, and yet we are hosting the G7 summit in the UK in June. “Diplomatically, it is imperative that the prime minister is able to bring our allies to the table to kick start the global recovery, combat Covid and avert climate breakdown.” The government is refusing to put plans to cut aid from 0.7% of gross national income to 0.5% to a Commons vote, although legal advice given to Tory MPs suggests that a decision to miss the target deliberately may be unlawful and a potential subject of judicial review. The legality of Johnson’s actions has been challenged by the former solicitor general Lord Garnier and in a legal opinion commissioned by rebel Tory MPs from the former director of public prosecutions Lord McDonald. No 10 has been warned by the rebel MPs that it may not want a damaging judicial review in the midst of the high-profile British chairmanship of the G7 summit in June. The warning was made by Liz Sugg, who resigned as an FCDO minister in protest at the cuts to aid. Lady Sugg said: “Britain, as a force for good, sets global standards and defends the rules-based international system. Legal opinion like this risks undermining our credibility on the world stage at the very moment we need to strike trade deals, negotiate communiques and agree ambitious legally binding climate targets. Cutting our aid and overseas investments sends a message that Britain is withdrawing from the world at the very moment we should be showing strong leadership.” The plea also came from the Conservative MP Neil Parish, chairman of the environment, food and rural affairs select committee, who said aid cuts risked becoming a lethal blow to the Cop26 summit in November. He said: “The job of a Cop president at UN summits is to act as a trusted figure at the heart of the talks. The cut to aid severely damages the trust that climate-vulnerable countries have in the Cop26 presidency. A U-turn on the aid cut would go a long way to restoring much-needed trust and solidarity between developing countries and the Cop26 presidency.” Ministers say the UK aid programme will still be higher as a proportion of gross national income than the majority of G7 countries, and climate finance will be treated as a priority. But earlier this month, a government body called UK Research and Innovation wrote to businesses, higher education and research institutions to inform them that cuts to overseas development assistance would leave a £120m hole in funding for the year 2021-22. One of the projects threatened by the cuts aims to enhance the role universities play in addressing climate. The UK has added South Africa to the list of the non-G7 countries invited to the June summit. India, South Korea and Australia had already been invited, but there had been concern that the lineup had started to give the impression of an anti-China diplomatic alliance.