Anger is growing over the government’s decision to merge the overseas aid department with the Foreign Office, with senior Tories and ex-ministers demanding Boris Johnson install a development minister in the cabinet. The Conservative former secretary of state for the Department for International Development (DfID) Andrew Mitchell is among the signatories to a cross-party letter sent to the prime minister that also calls for the retention of the Commons international development committee (IDC) and the scrutiny body, the Independent Commission for Aid Impact (ICAI). More than 70 parliamentarians have signed the letter led by a former IDC chair, Lord Malcolm Bruce, to say scrutiny on aid following the sudden merger is vital and the UK must show it is “not turning its back on the world’s poorest”. Bruce, a Liberal Democrat peer who chaired the committee for a decade from 2005 to 2015, said: “The new proposals abruptly announced without consultation have caused dismay across all parties, including your own. “Adopting the measures we are proposing would go a considerable way to reassuring those who wish to maintain the UK’s world leadership on development and the soft power benefits it brings. “It would also give a strong signal that the new arrangement will not lead to the UK abandoning its commitments to the poor people of the world living in low income countries.” The government announced it was merging DfID, which has a budget of around £15bn, with the Foreign Office earlier this month. The new Foreign, Commonwealth and Development Office will be set up in the autumn. DfID was set up by Tony Blair and many Conservatives have long called for it to be axed. Last week Johnson disparagingly said it had been “treated as some giant cashpoint in the sky that arrives without any reference to UK interests”. Mitchell established the ICAI while he was secretary of state between 2010 and 2012. It is an independent public body that scrutinises British aid spending. Tory peers who have signed the letter also include former health secretary Lord Lansley and former Welsh minister Lord Bourne. Also joining the call were the current IDC chair, Labour MP Sarah Champion, and the former DfID ministers Lord Triesman, a crossbencher, the Lib Dems Lady Featherstone and Lady Northover and Labour’s Lord Foulkes. Champion said the simplest way to ensure proper oversight of UK aid spend was to expand the committee she chairs. “At the moment, the plan is to expand the foreign affairs committee. But ODA [overseas developments assistance] spend cuts across many different departments. You need a committee that has that reach,” she said. The foreign affairs committee, which is chaired by Tom Tugendhat, is already working on six inquiries. ODA, which is governed by four different acts of parliament, has to alleviate poverty as well as delivering “value for money for the taxpayer” she said, all of which requires independent scrutiny. The committee’s interim report into the effectiveness of aid, published earlier this month, argued strongly that an independent aid-giving department with a cabinet-level minister leading its work was imperative if the UK was to help end extreme poverty.