When the most senior officials across Whitehall gathered for a rare away day on Friday, an attack on the impartiality of the civil service by a leading Brexiter ensured they had plenty to talk about between the presentations and flow charts.

Since the referendum there have been a string of allegations thrown at the politicians and institutions perceived as failing in their duty to deliver a clean break from the European Union. However, while pro-Remain MPs have largely been the target to date, the civil service is increasingly in the crosshairs.

Last week’s row erupted after Jacob Rees-Mogg, the leader of the pro-Brexit European Research Group of Tory MPs, suggested in the Commons that Treasury officials had deliberately drawn up economic models designed to undermine Brexit. Steve Baker, the influential pro-Leave minister, apologised for initially failing to challenge the claim – which made David Davis, the Brexit secretary, visibly wince.

Even before the spat, some senior Whitehall figures had already noticed a new tendency to lay the failures of the government’s Brexit policy at the civil service’s door. Just hours before Rees-Mogg made his allegations, Gus O’Donnell, the former cabinet secretary, was down the corridor in the Lords, telling peers that his former Whitehall colleagues were under attack. “It is particularly disappointing to see a divided cabinet resorting to attacking the civil servants who simply want to implement whatever policy cabinet finally decides upon,” he warned. “The bickering and blaming of civil servants needs to stop.”

The claim in today’s Observer by former cabinet secretary Andrew Turnbull that leading Brexiters have adopted similar tactics to the “stab in the back” myth – propagated in Germany after the first world war to suggest its military had been betrayed by internal forces – is the most incendiary description of Brexiter tactics. However, others have raised concerns about the willingness by some to attack pillars of Britain’s constitutional make-up – be it judges, politicians or officials. Andrew Cooper, formerly David Cameron’s pollster and a key figure in the Remain campaign, said Rees-Mogg’s attack showed that “hard-Brexiteers are the UK manifestation of bullying post-Truth Trumpite alt-right”. “Objective analysis is a conspiracy, actual facts met with alternative facts; considering risks and costs is treason, reporting them is fake news,” he said.

Facebook Twitter Pinterest Whitehall has been put in firing line by pro-Brexit cabinet members. Photograph: Jill Mead/The Guardian

Nick Macpherson, a former chief civil servant at the Treasury, tweeted yesterday: “First it was the socialists, then the unions, the immigrants and Brussels bureaucrats. Now it’s the treacherous Treasury. #fantasyisland.”

Many Whitehall insiders are prepared for even more heated rhetoric as Britain is forced to make Brexit trade-offs. Some opted not to speak out this week, keeping their powder dry for “when it goes really wrong”.

With cabinet ministers preparing for a two-day crunch meeting this week over the Brexit deal, some officials believe the attacks on Whitehall are actually a proxy, designed to remind those gathered to deliver a meaningful Brexit.

Meanwhile, Rees-Mogg, Tory grassroots favourite for leadership, yesterday stood by his claim that in drawing up its Brexit plans, the Treasury was trying to influence the argument. He also said that Charles Grant, head of the Centre for European Reform, had been given improper briefings. “He is getting private briefings from the Treasury against government policy,” he told BBC Radio 4’s Today. “This is very serious. It is not for officials to invent policy.

“With the referendum and with the EU, the Treasury has gone back to making forecasts. It was politically advantageous in the past. It is the same for them now. I do think they are fiddling the figures.”

Grant said it was perfectly normal for officials to talk to think tanks. “The Treasury cares about economics so it is naturally pushing for the sorts of Brexit that minimise the economic damage,” he said.