The Prime Minister has insisted an exit from the European Union is not "the right answer" and he is "close" to securing a renegotiation deal.
In an interview on the BBC's Andrew Marr Show, David Cameron said "it's a hard work" but that he was "confident we can get a good outcome".
"I am hopeful of a deal in February and if we do that we can go ahead and hold the referendum", he added.
I'm determined to fulfill what we put in our manifesto which is the renegotiation, the referendum. I think the best answer for Britain is staying in a reformed European Union if we can get those changes, but as I've said before and I'm happy to say again if we don't get them I rule nothing out. By saying nothing out I absolutely mean that.
When asked if the Government was preparing contingency plans for a so-called Brexit, Mr Cameron said:
"I don't think that is the right answer for the reasons I have given. Were that to be the answer we would need to do everything necessary to make that work."
"The civil service are working round the clock to support my negotiation", he added.
Summary: Cameron's EU demands
Mr Cameron also said he would allow Eurosceptic ministers to campaign for Brexit in a "personal" capacity, adding, it has "always been my intention".
He also said would not resign in the event he loses an in/out referendum.
Tory backbencher David Davis told the BBC's Sunday Politics he expected up to half the parliamentary party and "five or six" Cabinet ministers to campaign for Brexit.
He also called the lack of planning for the UK leaving the EU "disgraceful".
"This is actually disgraceful. Because you know, you've got two moderately likely outcomes, we don't know which it will be," he said.
Economic governance - To ensure any measures taken by Eurozone countries to secure the long-term future of their currency "respect the integrity of the Single Market, and the legitimate interests" of the UK and other non-Euro members.
Competitiveness - Write "competitiveness into the DNA" of the whole European Union.
Sovereignty- An end to Britain's obligation to work towards an "ever closer union" which is agreed in a "formal, legally-binding and irreversible way"
Immigration - Greater control on arrivals from inside the EU