Leading Brexiters who accuse civil servants of sabotaging Britain’s exit from the EU are adopting dangerous tactics similar to those of rightwing German nationalists between the two world wars, a former head of the civil service has warned.

In a stark assessment of the acute tensions developing over the issue, Andrew Turnbull, who led the civil service under Tony Blair, said that Whitehall officials had become the victims of “pre-emptive scapegoating” by Brexiters who feared they were losing the argument.

Jacob Rees-Mogg, the new leader of the European research group of Eurosceptic Tory MPs, has suggested that Treasury officials could be deliberately trying to frustrate Brexit. Yesterday he repeated a claim that the Treasury was “fiddling the figures” to emphasise the downside of a “hard” Brexit in which Britain would leave both the single market and customs union.

Former chancellor Nigel Lawson also recently claimed that officials would attempt to frustrate Brexit because they were opposed to “radical change”.

Lord Turnbull is among a number of senior figures concerned about attacks on the civil service, with many worried that the atmosphere will deteriorate further as more difficulties emerge.

Robin Butler, another former cabinet secretary, said he believed the actions were part of a deliberate “Brexiteer process of intimidation”.

Turnbull told the Observer that the attacks on Whitehall were reminiscent of the “stab-in-the-back” myth, which emerged in Germany after the first world war and was later taken up by the Nazis.

Tory Brexiter Jacob Rees-Mogg has suggested Treasury officials could be deliberately trying to frustrate Brexit. Photograph: David Levenson/Getty Images

“‘Dolchstoss’ means ‘stab in the back’,” he said. “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.

“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.”

Tensions are running high before a crucial week for Brexit, during which the prime minister and key cabinet ministers will meet over two days to hammer out details of a final deal that can keep all Tory factions on board. The stakes are high, with Theresa May under huge pressure to make her plans clearer.

Insiders said officials were examining options that would reduce delays at the UK’s border without keeping it fully inside the EU’s customs union. The crunch point is whether there is any way Britain can strike up a customs agreement that stops chaos at the border but also allows some flexibility for the government to sign its own international trade deals.

Rees-Mogg made clear yesterday that there could be no limits placed on Britain’s ability to strike deals. He repeated his claim that the Treasury’s Brexit models were politically influenced.

Butler said there was a “movement among the rabid Brexiteers to point the finger at the civil service, which I think is completely unjustified”.

He added: “It is unwise on the part of the Brexiteers, because the government can’t do this operation without the civil service. To demonise them isn’t really very sensible.”