Civil servants will not be allowed to support ministers who disagree with the official government line on Britain's place in the European Union in the forthcoming referendum, David Cameron has announced.
The prime minister is currently seeking to renegotiate the UK's position in the EU and has promised an in-out vote on membership by 2017.
In a highly unusual move, the prime minister last week made clear that while "a clear government position" will be formed after the renegotiation with fellow European leaders, individual ministers will be able to campaign for the opposing side while staying in government. The decision effectively suspends the convention of collective ministerial responsibility, where members of the Cabinet are expected to speak with one voice in public.
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But in a letter to ministers published on Monday, Cameron made clear that ministers who do choose to oppose the government position – which is expected to urge voters to back staying in a reformed Europe – will have to do so without the support of departmental officials.
The prime minister said it would remain the "duty of the civil service" to support the government's position "in the normal way", in spite of the exceptions granted to ministers with "long-standing and sincerely held views".
Cameron added: "It will not be appropriate or permissible for the civil service or individual civil servants to support ministers who oppose the government's official position by providing briefings or speech material on this matter."
Instead, the prime minister confirmed, ministers at odds with the government line will have to rely on the "personal help and advice" of their political special advisers, so long as that "does not draw on official or departmental resources".
Cabinet secretary Sir Jeremy Heywood will provide separate guidance to civil servants outlining their duties during the referendum, Cameron confirmed, as he urged ministers to "treat each other with appropriate respect and courtesy" during the campaign.
"We all recognise that the UK's membership of the EU is an issue on which some colleagues have long-standing, depply-held positions of conviction – hence my decision to set aside, on a highly expectional basis, the normal rules of collective responsibility," the prime minister said.
"But throughout this period, and in its aftermath, we will continue to have responsibility for governing the country and serving the public who elected us. This can only be done effectively if we remain, despite differences on this one issue, a united, harmonious, mutually respectful team."
Civil service neutrality in the run-up to the EU vote was the subject of the government's first Commons defeat of the parliament in September last year.
More than 30 Conservative rebels sided with Labour to throw out plans to change the rules preventing official resources from being used to publish "promotional material" in favour of one side in an election or referendum.