Cabinet secretary Sir Jeremy Heywood is to face questions from MPs this week amid claims that ministers in favour of leaving the European Union are being put at a disadvantage by rules governing their access to civil service support.
The official government position ahead of June's EU referendum is in favour of Britain saying in, under a renegotiation deal secured by prime minister David Cameron.
But the usual rules of collective responsibility – which mean ministers are bound to publicly back the government line – have been suspended on the EU issue, allowing Cabinet ministers ncluding justice secretary Michael Gove and work and pensions secretary Iain Duncan Smith to campaign for a vote.
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However, Heywood, the head of the civil service, issued guidance to officials last week, making it clear that ministers who do back an exit will not receive full civil service support.
While the guidance says departments should "continue to provide support in the normal way to ministers operating in their ministerial capacity", it says it "will not be appropriate or permissible for the civil service to support ministers who oppose the government's official position by providing briefing or speech material on this matter".
Ministers in favour of an exit are also not permitted to see official departmental papers relating to the referendum question – apart from those they have already seen – and must rely instead on their political special advisers for research support.
The commons Public Administration and Constitutional Affairs Committee – chaired by prominent eurosceptic Conservative Bernard Jenkin – will tomorrow question Heywood on the guidance. Jenkin told The Guardian that Heywood's guidance was "unorthodox and unprecedented", saying that ministers were "indivisible from his or her department".
The hearing will come after a number of eurosceptic cabinet ministers took to the airwaves to speak out against the guidance, claiming the rules could have an impact on the running of departments.
Work and pensions secretary Iain Duncan Smith told the BBC at the weekend that he had doubts about how the rules would play out in practice.
"I think that this can't possibly apply in the sense of us not knowing what's going on in the department because we are responsible for the department and, for example, I will have to work on these proposals that came back from the recent negotiations if we vote to remain in we will have to deliver that," he said.
His pro-Brexit cabinet colleague Chris Grayling, the leader of the Commons, on Monday said there should be "nothing that happens [that] can prevent a minister running a department – whether they’re on the side campaigning to stay in, or campaigning to stay out – from being able to do the job for this country and for this government".
But Cabinet Office minister Matt Hancock highlighted the distinction between referendum-related matters and the rest of government business, as he sought to defend the rules.
"It's very clear that we are, the government is, functioning on all questions other than specifically the 'In/Out' question, in the entirely normal way," he told the Today programme. "And then on the 'In/Out' question the government then has a position and ministers are then allowed to take a personal position that's different from that. There are no rules other than those set out last Monday in the letter from Jeremy Heywood."
That view was echoed by a Cabinet Office spokesperson, who said there was "no separate process for departments whose ministers are campaigning to leave the EU beyond the guidance published on Monday".
They added: "Day-to-day business will continue to be conducted in the usual way and all ministers will retain access to any papers relevant to their departments other than those specifically regarding the in-out question.”
Ahead of Heywood's committee appearance this week, there are signs that Commons speaker John Bercow will on Monday grant an urgent Commons question on the guidance, forcing ministers to come to the chamber and directly respond to MPs' concerns.