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MPs vowed to fight the closure of Britain’s aid department “every step of the way” amid fresh fears a controversial Whitehall merger will see scrutiny of the government “cut to the bone”. 

Dominic Raab confirmed in June that the Department of International Development would be scrapped and merged with the Foreign Office. 

Boris Johnson drew fury from MPs, charities and his own backbenchers after saying the new Foreign Commonwealth and Development Office (FCDO) would stop the UK being used as a “giant cashpoint in the sky”.

Opponents say the UK should be strictly neutral when spending to eliminate poverty but the government says money could be better used to “promote British influence around the world”. 

The department is being created as the UK breaks from the EU and develops its own trading policy but Raab, the foreign secretary, has insisted no aid will be “tied” to contracts or trade deals. 

But a letter from Raab to the Lib Dems has prompted fresh concerns about oversight of the merger and the new department’s policy objectives. 

Raab revealed the integration will be overseen by Mark Sedwill, despite the cabinet secretary leaving Whitehall in September. 

He also failed to outline how aid will be distributed in future, stoking concern that international development cash will in fact be tied to trade. 

The letter says only that the new department will be “guided by” the International Development Act and citing “a commitment” to poverty reduction – which was a key strain of DfID’s mission. 

The minister says spending 0.7% of national income on aid is “enshrined in law”, but adds “we will continue to look at how this money can be spent most effectively in our national interest”. 

It was also unclear whether the government’s aid spending would be scrutinised by Independent Commission for Aid Impact or a parliamentary committee. 

Raab also says that “fully costed plans are being developed”, suggesting the government still does not know how much money the merger will save or cost. 

The minister also confirms “there are no plans for a second secretary of state” and that the department will be led by one senior civil servant and one executive board.  

He adds: “The FCDO will have oversight of the government’s aid policy and I will take final decisions in line with the UK’s international and domestic objectives.”  

Wendy Chamberlain, the Lib Dems’ spokesperson on international development, said: “For countless vulnerable people in need around the globe, UK international aid has made a vital difference. We should be proud of that.

“Instead, we have Dominic Raab cooking up some half-baked plan with oversight from someone who has one foot out the door. If Brexit is anything to go by, Raab cannot be trusted to protect international aid.

“Reducing global poverty should never be a political choice. Ministers must therefore make clear how they will protect aid, including committing to retaining ICAI, the International Development Committee and a development minister in cabinet.

“If the government won’t listen, then there is the will among opposition MPs to fight ministers every step of the way.”  

Nick Dearden from the campaign group Global Justice Now, meanwhile, called the letter “alarming”, adding “measures to reduce poverty” should not be “mixed up with the urge all governments have to promote British interests, British business and British investment”. 

He said: “Dominic Raab getting his hands on a £15bn budget to, as he sees it, project Britain’s influence around the world, is absolutely terrifying frankly.” 

He added: “It’s extraordinary that the government keeps talking about making aid more accountable, because again, this move is precisely the opposite. They’re abolishing a secretary of state who was legally accountable for ensuring that aid spending reduces poverty around the world.

“They’re abolishing the parliamentary committee whose sole purpose was to oversee this. And we still don’t know the fate of the independent watchdog for aid spending. Accountability has been slashed to the bone.” 

Raab finishes his letter by saying: “This government is unashamed in believing that its job is to promote British influence around the world, to try and change the world for the better, and to get the best value for the British taxpayer who spends so generously to help others. 

“This change will help us do that.”