David Cameron has spelled out to ministers that they will not be able to campaign for a British exit from the European Union until after the negotiation process is complete.
The Prime Minister called for ministers on both sides of the argument to "treat each other with appropriate respect and courtesy" in a personal minute setting out the "wholly exceptional" rules which will allow members of the Government to support Brexit once the talks have finished.
The "special arrangement" will allow individual ministers to take a different position from the official Government line after a Cabinet discussion, which will follow the conclusion of talks between Mr Cameron and his fellow EU leaders.
The Prime Minister hopes to strike a deal on his demands at a crunch summit in Brussels next month which will then allow him to recommend that the UK remains within a reformed EU, but until the talks are concluded he stressed that all his ministers should follow the Government line.
In the minute sent to ministers, the Prime Minister said: "Until that point - when it will become clear whether a deal can be negotiated that delivers the objectives I have set out - all ministers should continue to support the position set out in our manifesto and say or do nothing that will undermine the Government's negotiating position."
Officials would be expected to support the Government's stance and "it will not be appropriate or permissible for the civil service or individual civil servants to support ministers who opposed the Government's official position".
But ministers who oppose the official position would be able to draw on personal help and advice from their special advisers, known as spads, as long as it is in line with their wishes and "in their own time".
Mr Cameron's message set out that the "wholly exceptional arrangement" will apply only to the question of whether to remain in the EU or to quit.
"All other EU or EU-related business, including negotiations in or with all EU institutions and other member states, and debates and votes in Parliament here on EU business will continue to be subject to the normal rules of collective responsibility and party discipline," he said.
But Mr Cameron acknowledged that "we will need to be flexible and apply common sense", and Eurosceptic ministers will not be expected to "contradict" their positions in Parliament.
"If, as I hope, the negotiation is successful and the Government is able to recommend that we should remain in a reformed EU, and this special arrangement comes into place, ministers who choose to depart from the Government's recommendation because of long-standing and sincerely held views will not be expected directly to contradict such a position while otherwise defending government policy in Parliament."
Setting out the restrictions on civil servants, Mr Cameron said officials would not be allowed to support ministers who oppose the official line "by providing briefings or speech material on this matter", but spads would be able to help until the last 28 days of the campaign.
The Prime Minister accepted that ministers should be allowed to campaign for Brexit to avoid a damaging split within his Cabinet and in his minute he acknowledged that some of his colleagues had "deeply-held positions of conviction" on the issue.
In an attempt to avoid a repeat of the infighting over Europe which has torn previous Tory administrations apart, Mr Cameron said: "It will be very important during this period for ministers on both sides of the debate to treat each other with appropriate respect and courtesy.
"We all recognise that the UK's membership of the EU is an issue on which some colleagues have long-standing, deeply-held positions of conviction - hence my decision to set aside, on a highly exceptional basis, the normal rules of collective responsibility.
"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."
Earlier, Mr Cameron insisted it would be a "great prize" for the UK to remain in the EU after "knocking on the head the things that have been driving us up the wall" about Brussels.
"That's the prize that the Government is aiming for," he said.
Conservative former cabinet minister Owen Paterson said: " It's welcome that ministers who want to campaign to take back control from the EU will be able to do so without resigning, but it's increasingly clear that it'll be one rule for those who want to stay in the EU at all costs, and another rule for the rest.
"Ministers who wish to extol the virtues of the EU have been given a green light to do so already, while those who want to take back control are currently gagged and will only be allowed to speak from the backbenches.
"It looks like the Government is focusing its energies on gearing up the full weight of the Whitehall machine to campaign to keep us in the EU rather than on bringing powers back from Brussels."
Liz Bilney, chief executive of the Leave.EU campaign, said: "The question of Cabinet collective responsibility is a distraction from the truth that the Prime Minister's negotiations are utterly worthless, as he asked for nothing substantial and will be granted nothing substantial.
"Cabinet ministers should have been rejecting the Prime Minister's fudge already, just like so many of his backbenchers and former ministers have been doing in the last few weeks.
"How long will this charade last? If there is no agreement in February, will Cabinet EU-sceptics continue to sit on their hands? It all goes to show why the campaign to leave the EU must belong to the people and not politicians living in the disconnected world of the Westminster bubble."