Cabinet secretary, who accused of constitutional impropriety, is expected to be questioned in the Commons about the procedure

Sir Jeremy Heywood, the cabinet secretary, is facing allegations that he is acting in a constitutionally improper manner as Whitehall sources confirmed that senior civil servants are being told to bypass ministers who want to leave the EU.

Bernard Jenkin, the chairman of the Commons public administration select committee, said Heywood appeared to be acting in an “unorthodox and unprecedented” manner.

Heywood is expected to face pressure on Monday amid signs that John Bercow would grant an urgent question in the Commons about guidelines banning civil servants from showing official papers related to the EU referendum to Brexit ministers.

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In a move aimed specifically at Iain Duncan Smith, Heywood issued new guidelines last week to ban civil servants from preparing new research for anti-EU cabinet ministers that could be used in the EU referendum campaign. No 10 had feared that Duncan Smith, who has strong doubts about the welfare elements of the prime minister’s EU reform plan, would seek to ask his officials to assess the credibility of the plan.

Senior Whitehall sources said Heywood had gone further and advised the most senior civil servants in departments headed by Brexit ministers that there would be occasions when they would have to bypass their ministers and deal solely with him.

At least one permanent secretary is understood to have raised concerns with their Brexit secretary of state that Heywood may be acting in a constitutionally inappropriate manner because secretaries of state, technically at least, are solely responsible for their departments under a seal granted by the Queen.

Officials in Heywood’s office are also contacting the private offices of ministers who have yet to declare which side they are supporting in the referendum, asking to make their intentions clear. This is designed to work out whether they are entitled to see all papers in their department related to the referendum. Duncan Smith urged David Cameron to reverse the Heywood guidelines.

The Brexit ministers hoped No 10 would face strong pressure to back down on the Heywood guideline on Monday following signs that the Speaker would grant an urgent question to Bernard Jenkin. The chairman of the commons public administration select committee declined to comment on whether he was seeking to table the question.

But Jenkin said that any attempt by Heywood to bypass a secretary of state would be unconstitutional and could be unlawful by infringing the Carltona principle, which says that officials in a department work “under the authority of ministers”. Jenkin, whose committee will question Heywood on Tuesday, said of the cabinet secretary’s guidelines: “This is unorthodox and unprecedented. In law the minister is indivisible from his or her department.”

In calling for the ban to be reversed, Duncan Smith told the BBC’s Andrew Marr Show: “I think that this can’t possibly apply in the sense of not knowing what is going on in the department because we are responsible for the departments.”

Philip Hammond, the foreign secretary, defended the ban. He said: “Those ministers who want to argue another case are being allowed to do so but the civil service can’t support them in doing that. They’ll have to find their own external support.”

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The row over the role of Brexit ministers came after the leave camp were angered by a personal attack on Boris Johnson in the House of Commons last Monday. Cameron suggested that the mayor of London had decided to campaign to leave the EU as a way of boosting his chances in the Tory leadership contest.

Duncan Smith advised Cameron to focus on the issues and to step back from personal attacks. He said: “The prime minister deserves some credit. This is a generous offer to let cabinet ministers break ranks and debate this because it is the biggest issue. But the general view at the time and I think should remain now is don’t play the person, play the ball. We should take a deep breath and ask ourselves a simple question. This is about Britain not us.”

However, he accused the prime minister and George Osborne of talking down Britain after they issued a series of warnings about the threat to the economy if the UK voted to leave the EU. “I say this to those who want to remain in: I have never heard such a lot of pessimistic downsizing of Britain. Britain is a phenomenal country, the fifth largest in the world. It has stood alone and fought for freedom, it has traded, it has been a global trader. It can yet again be a global trader. Why would we have such a low opinion of the British people that we go out and talk about leaping into the dark, we talk about profound shocks? We talk about being too small. I have a different view. Britain is a great country.”

A Cabinet Office spokesman said: “The cabinet secretary and his office are in regular contact with permanent secretaries and private offices on a range of issues.

“The prime minister made an exceptional exemption to collective responsibility on the specific issue of the referendum question, and the guidance makes a clear distinction between ministers campaigning to leave the EU and those campaigning to remain. Departments and the Cabinet Office therefore need to know which ministers will be subject to the new processes.



“There is no separate process for departments whose ministers are campaigning to leave the EU beyond the guidance published on Monday. 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.”