Britain has a proud track record of supporting the world’s poorest through its aid commitments. This is not only morally the right thing to do, it is also the smart thing to do.

This cast-iron commitment to the poorest indirectly creates significant soft power for Britain. Disrupt this commitment by merging the Department for International Development (DfID) into the Foreign Office and diverting more aid to UK national interest, and you produce a lose-lose: the world’s poorest (wrongly) suffer, and significant British soft power immediately drains away, at precisely the time when the country is trying to redefine its role in the world.

As one senior British diplomat said to me: “Our influence in the UN comes from three things: our permanent five status on the security council, the English language … and our 0.7% commitment.”

The food and medicine DfID funds not only saves lives, it spreads goodwill for Britain across the world (including in many countries we want to do post-Brexit trade deals with). It sends a clear message about British values – we are outward-facing, tolerant, compassionate, respecting of democracy, the rule of law and human rights – and opens doors at the highest levels, strengthening our hand in global diplomacy.

As Justine Greening’s special adviser while she was international development secretary, I saw this first-hand. I lost count of the number of meetings I sat in at the UN where the room spontaneously erupted into applause at the mention of Britain’s 0.7% commitment.

But the reason it elicits such a response is because it is a genuine commitment to the world’s poorest – supported by the holy trinity of DfID’s world-class reputation, its status as a standalone department with a secretary of state, and Britain’s use of the internationally-agreed aid rules.

There’s a good reason why the latest Portland index on soft power notes that merging DfID into the Foreign Office is “unlikely to be positive” and why Joseph Nye, the Harvard academic and founder of the soft power concept, said: “The best propaganda is not propaganda.” A merger with the Foreign Office or loss of DfID’s secretary of state would signal a hollowing out of our longstanding poverty-first commitment, an end to Britain as a development superpower, and a resulting significant loss of soft power.

We all also want taxpayers’ money to be spent well. As Bill Gates said: “DfID is widely recognised as one of the most effective, efficient, and innovative aid agencies in the world”. It is also the most scrutinised government department, with its own watchdog, the independent commission for aid impact, in addition to a select committee and the national audit office – and it ranks third globally in the aid transparency index. The Foreign Office ranks 40th out of 45.

DfID’s world-class reputation also means it attracts development officials at the top of their game, who are passionate about helping the world’s poorest and tailoring programme spend accordingly. It is fantastic that the prime minister personally champions “12 years of quality education” for the world’s poorest girls, but only DfID staff have the skills to help the world achieve this. Despite DfID spending more than 70% of the government’s aid budget, a disproportionate number of “aid scandal” stories splashed in the papers come from aid spent by other departments. UK aid works because DfID works.

DfID’s spending echoes what the British people want. Polling consistently shows that the public – including Conservative voters – want our aid budget spent on the world’s poorest, not on promoting domestic interests. I hope data-driven Dominic Cummings has clocked this.

To effectively project Global Britain in the years ahead, there is no doubt the three Ds – defence, diplomacy and development – need to work more closely together, arguably helped by a better-funded Foreign Office, as well as a continued commitment to spend 2% of GDP on defence. The most effective way to achieve this is through separate departments, staffed by people with relevant skills, run by separate secretaries of state, who are then effectively coordinated through a strong and active National Security Council.

As the UK redefines its role in the world, we have the opportunity to consider what sort of nation we want to be. Of all the challenges Boris Johnson and Cummings could direct time, energy and resources to, why disrupt a high-performing department that saves lives, and through doing so gives Britain significant clout on the world stage?

Simon Bishop was special adviser to Justine Greening from 2014 to 2016. He is currently deputy CEO of Plan International UK