Up to five Cabinet ministers will campaign for Britain to leave the European Union and David Cameron should allow them to speak out now, a senior Tory said as the Prime Minister steps up his drive to sell the proposed deal.
Mr Cameron will make a statement in the Commons on the draft deal thrashed out with Brussels, giving him a chance to gauge reaction to the plan - drawn up with European Council president Donald Tusk - from his own MPs.
Former defence secretary Liam Fox said he was "certain" that four or five serving Cabinet ministers would eventually come out in favour of Brexit, but he warned the PM that if he suppressed opposition to the EU until after any deal was done, he risked creating a lasting split in the Tory Party.
Mr Cameron'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 was thought to be the most senior Cabinet minister considering opposing the plan and had been tipped as a possible leader of the Out campaign in the forthcoming referendum on Britain's EU membership - 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."
He added: "I don't know exactly how many, but I can think of four or five for certain."
The Prime Minister's Commons statement follows a speech on the proposed deal on Tuesday and Dr Fox said Cabinet opponents should also be allowed to express their views in public.
Under the rules set out for the referendum, ministers will be allowed to campaign on the opposite side from the Prime Minister but only after a Cabinet meeting following the conclusion of any deal.
Dr Fox said: "The agreement has been that no-one will make the case for or against until there is a final agreement at the European Council.
"That would be fine if it applies equally to both sides. The danger is always that the rules that apply are seen to be different for one side of the argument than the other.
"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.
"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 his appearance on Tuesday, Mr Cameron said there was still a lot of work to do to finalise the agreement ahead of a crunch meeting of EU leaders in Brussels on February 18 and 19.
However, he made clear that he believed the fundamental elements were in place for a deal which he would recommend voters accept when the referendum is declared.