David Cameron is facing calls to allow Cabinet colleagues to start campaigning for withdrawal from the EU, as he steps up his drive to sell a package of proposed reforms.
Former defence secretary Liam Fox predicted that up to five Cabinet ministers will campaign for Brexit in the upcoming referendum, and warned that the Prime Minister risks creating a lasting split in the Conservative Party if he tries to gag them any longer.
European Commission president Jean-Claude Juncker hailed the draft deal unveiled on Tuesday as "fair for the UK and fair for the other 27 member states".
But he risked antagonising Eurosceptics by saying that the euro "remains the currency of the EU" and that a proposed emergency brake on migrant benefits will be "limited in time" and would apply only in "exceptional circumstances".
The brake would help address a situation created by the UK Government's own failure to apply transitional restrictions more than a decade ago, he told the European Parliament.
After the draft deal drawn up with European Council president Donald Tusk received a broadly hostile reaction from the right-leaning press, Mr Cameron has an opportunity to gauge the response of his own MPs as he delivers statement to the House of Commons.
The Prime Minister's position received a major boost on Tuesday when Home Secretary Theresa May signalled she could be prepared to support the proposals, saying they provided "a basis for a deal".
Mrs May had been tipped as a possible leader of the Out campaign in the in/out referendum - now expected to be held in June.
However, in a statement, she said it was "encouraging" that key UK concerns about the "abuse" of EU free movement rules and the use of European law to block the deportation of foreign criminals were being addressed.
Disappointed Out campaigners may now look to London Mayor Boris Johnson - who has yet to declare which side he will support - to spearhead the drive for Britain to leave.
Responding to Mrs May's statement, Dr Fox, a prominent Eurosceptic, said: "I'm sure Theresa May, as with all my other colleagues, will make up their own minds."
He said the offer on the table meant that "what we can get, at best, is better membership of the wrong club".
Dr Fox told the BBC Radio 4 Today programme: "I think there will be a number of Cabinet ministers with a range of different responsibilities who will want to be in the Leave camp ... I don't know exactly how many, but I can think of four or five for certain."
Mr Cameron has told ministers he will suspend the principle of collective responsibility to allow them to campaign on either side of the debate, but not until a Cabinet meeting following the conclusion of any deal, which could come at a Brussels summit on February 18-19.
But Dr Fox suggested that the PM himself already appeared to be campaigning in favour of the deal in a speech he delivered on Tuesday in which he said the reforms were "worth fighting for".
"If the Prime Minister has already decided that the draft deal is enough for him to campaign, to go out there selling the deal, then it should be for others who don't agree with that to make their own case," said the North Somerset MP.
"I think the danger of treating the two sides differently is that it will make it more difficult for us to come together after the referendum."
In Strasbourg, Eurosceptic MEPs were scathing about the package, with the DUP's Diane Dodds dismissing it as "a smoke-and-mirrors charade" and Independent Janice Atkinson as "a Chamberlain moment" - in an apparent reference to the doomed 1938 attempt to forge a peace deal with Hitler. Ukip leader Nigel Farage said that "people power" and not politicians would decide the UK's future relations with Europe.
But the Conservative leader of the ECR grouping, Syed Kamall, insisted the deal was "a good place to start" in debating "matters that should benefit all European Union countries". And the sole Liberal Democrat MEP Catherine Bearder said staying in the EU would be "better for our prosperity, our security and our environment".
Meanwhile, venerable Tory thinktank the Bow Group warned Conservative MPs who campaign to remain in the EU could face deselection when seats are reallocated under planned boundary changes.
Pointing to a recent poll suggesting 71% of party members back Brexit, Bow Group Chairman Ben Harris-Quinney said: "Conservative Associations will be unforgiving towards any MP who thinks they can say one thing in an election pledge, and do another when in Parliament."