Prime Minister David Cameron has warned ministers not to "undermine" his efforts to reform the European Union.
In a letter to ministers released this afternoon by Downing Street, Cameron repeated his commitment to allow ministers to have a "free vote", and campaign with their conscience in the run-up to the EU referendum. But Cameron was clear in the letter that ministers would not be able to oppose the official government position until after an EU reform deal is reached.
"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 our position set out in our manifesto and say or do nothing that will undermine the government's negotiating position," Cameron wrote.
The Prime Minister has promised to hold a referendum by the end of 2017, following a period of renegotiation.
Cameron has repeatedly said that he is hoping to finalise a reform deal at next month's European Council meeting, and while he has yet to set a date for the in/out vote, punters are increasingly eyeing up this September.
In the letter to ministers, Cameron also stressed that the "wholly exceptional arrangement" of a free vote will only apply to the question of whether Britain should remain in, or leave, the EU.
"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.
Cameron also confirmed that civil servants would still be compelled to support the government position in the run-up to the referendum, but added that special advisers would be able to provide "personal help and advice" to ministers who oppose the government.
Eurosceptics questioned Cameron's intervention, with former Cabinet minister Owen Paterson saying: "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."