DAVID Cameron has called on his ministerial colleagues to show “respect and courtesy” to each other as they find themselves on differing sides during the European Union referendum campaign.

In a memo to UK Government ministers, the Prime Minister made clear they would not be able to campaign for a British exit until after the negotiation process was complete and that it was important his administration remained a "a united, harmonious, mutually respectful team".

At the weekend, Mr Cameron struck an optimistic note, saying he believed a deal with his 27 EU counterparts was closer than it had been and he remained hopeful of securing agreement at the February Brussels summit. This could pave the way for a referendum in mid-June.

In the personal note to colleagues, the PM called for ministers on both sides of the argument to "treat each other with appropriate respect and courtesy", setting out the "wholly exceptional" rules which would allow members of the Government to support Brexit once the talks had finished.

The "special arrangement" would allow individual ministers to take a different position from the official Government line after a Cabinet discussion, which would follow the conclusion of talks between Mr Cameron and his fellow EU leaders.

"Until that point,” he wrote, “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".

Mr Cameron's message set out that the "wholly exceptional arrangement" would apply only to the question of whether to remain in the EU or to leave it; all other EU business would continue to be subject to the normal rules of collective responsibility and party discipline.

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.

In an attempt to avoid a repeat of the infighting over Europe which has torn previous Tory administrations apart, the PM 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.”

Owen Paterson, the Conservative former cabinet minister, welcomed that ministers who wanted to campaign to “take back control from the EU” would 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,” he declared.

"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," added Mr Paterson.