In the space of a single week earlier this year, Tony Blair argued that government departments should be led by ministers recruited from outside of Parliament. Reform UK unveiled plans to give ministers greater powers over senior civil service appointments. At the same time, the government continued advancing its own reform agenda, including efforts to bring more outside expertise into Whitehall.

Different parties and politics. And yet on this point they seem to be remarkably aligned: Britain needs more people from beyond Westminster and Whitehall to help run the state. They could well be right.

What is more striking, however, is how little of the current debate engages with the evidence accumulated over decades of trying exactly this.

Britain has been attempting to bring more external expertise into government since the Fulton Report in 1968. More than half a century later, the Institute for Government still concludes that Whitehall struggles to attract, retain and properly use specialist knowledge from wider society.

The difficulty is that politicians often talk about ‘bringing in outsiders’ as though it means one thing. It doesn’t. Recruiting technical specialists into the civil service, appointing an external leader to run a major government function, and bringing ministers into government from outside Parliament are entirely different propositions. Each action raises …