The former head of the civil service has compared pro-Brexit MPs who have questioned the impartiality of government officials to "snake oil sellers" who can't handle their ideas being scrutinised.
Sir Gus O'Donnell told the Peston on Sunday show that recent attacks on the independence of the civil service by some were unfair.
"If you were to take a civil servant and cut them half – and let's be honest there's a lot of MPs who'd love to do this – like a stick of rock, you would see the honesty integrity and impartiality. That's the point – we look at the evidence and we tell it like it is," he said.
"But if you're selling snake oil, you don't like the idea of experts testing your products. And I think that's what we've got – this backlash against evidence and experts is because they know where the experts will go."
His comments came hours after Sir Andrew Turnbull, O'Donnell's predecessor as cabinet secretary under Tony Blair's second term in Number 10, told the Observer that leading Brexiteers had scapegoated civil servants and made a comparison to similar attacks made after the First World War in Germany.
“‘Dolchstoss’ means ‘stab in the back’. After the first world war there was an armistice, but the German army was then treated as the losers. Then, at the start of the Nazi era, the ‘stab-in-the back’ theme developed," he said.
"It argued that ‘our great army was never defeated, but it was stabbed in the back by the civilians, liberals, communists, socialists, and Jews’. This is what I think these critics are trying to do. They are losing the argument in the sense that they are unable to make their extravagant promises stack up, and so they turn and say: ‘Things would be OK if the civil service weren’t obstructing us’.
"When you don’t succeed, you find someone to blame for your failure."
On Friday, Brexit minister Steve Baker apologised to the House of Commons for appearing to agree with a question from pro-Brexit backbencher Jacob Rees-Mogg, who implied that there was an anti-Brexit conspiracy at the Treasury.
BuzzFeed News revealed on Monday that the government's own secret analysis of Brexit shows that the country would be worse off economically under every possible outcome of negotiations with the EU – sparking a running debate about the role and impartiality of independent evidence in government.