Prime Minister David Cameron has lashed out at Tory "pessimists" demanding immediate withdrawal from the European Union.
The Prime Minister said he believed it was "possible" to push through changes to the EU.
"I am faced as I do so, if you like, by two groups of pessimists," he said.
"There are some pro-European pessimists who say, 'you have to, in Europe, simply sign up to every single thing that anyone in the EU suggests.
"You sign every treaty, you sign everything - there is no alternative'.
"I think they are completely wrong.
"The second group of pessimists say there is no prospect of reforming the EU, you simply have to leave. I think they are wrong too.
"I think it is possible to change and reform this organisation and change and reform Britain's relationship with it."
Read more: Tory MPs plotting EU Commons vote
A group of Tory MPs will attempt to force a Commons vote over a referendum on the UK's European Union membership on Tuesday.
The Tory MPs backing the call for an EU referendum include:
- Hardline Eurosceptic MP Peter Bone has said he hoped to show the Tory leadership that there was "significant parliamentary demand" for the EU referendum pledge.
- Tory John Baron, who also tabled the amendment, organised a letter signed by dozens of Conservative MPs demanding referendum legislation.
Read more: Ex-chancellor calls for EU exit
- Former Cabinet minister Michael Portillo has followed ex-chancellor Lord Lawson in calling for the UK to leave the EU.
- Lord Lamont, another former Tory chancellor, joined the stampede of former Tory cabinet ministers saying it was possible for the UK to survive outside the EU.
- Nadine Dorries, the MP who was handed back the Conservative whip only on Wednesday, said she would be joining the rebellion.
Read more: Nadine Dorries wants EU exit
A group of Conservative MPs will attempt to force a Commons vote over a referendum on the UK's European Union membership next week.
The MPs are seeking to engineer a vote on an EU referendum by tabling an amendment to the Queen's speech.
Prime Minister David Cameron earlier defended his approach of seeking fundamental reform and holding a referendum on membership before the end of 2017.
Read more: Ex-chancellor calls for EU exit
Weekend opinion polls showed a clear public majority for cutting ties with Brussels as pressure mounted on David Cameron to set out plans for a referendum on the issue.
He faces a tricky summit on Thursday when leaders gather to thrash out the EU's future budget, and he has threatened to veto anything other than a real-terms freeze.
Labour joined forces with Tory rebels to inflict a Commons defeat on the Government by backing a real-terms cut in the 2014-20 package - leading to accusations of opportunism.
Labour could offer a referendum on Britain’s European Union membership at the next election, its policy director Jon Cruddas told The Daily Telegraph.
The opposition party would consider “in depth” whether to hand the vote to the public as it drafts its next manifesto, according to Cruddas, who is chairing Labour’s policy review.
“It’s something we will be looking at in depth in the policy review. At some stage there is going to have to be some resolution of what our relationship is here and what format that takes. It could be a referendum.
"We have said the time is not right as regards a referendum on Europe given the economics ricocheting around the eurozone. Obviously our position needs to be developed over the next period."
The paper claimed that Cruddas' comments would pile pressure on the Prime Minister, who is already facing calls from his party to give the public the EU vote.
The Prime Minister has hinted that the Conservative party may back a referendum on Britain's membership of the EU in the next parliament.
I don't think it is in Britain's interests to leave the EU but I do think what it is increasingly becoming the time for is a new settlement between Britain and Europe, and I think that new settlement will require fresh consent.
In the next parliament, I think there will be opportunities for a fresh settlement and for new consent to that settlement.
Labour leader Ed Miliband has accused David Cameron of having no clear position on whether there should be a referendum on Britain's membership of the EU.
Labour leader Ed Miliband has mocked David Cameron's stance on an EU referendum.
He told MPs that the Prime Minister was trying to appease the divisions in his own party, rather than acting in the interests of the nation.
Mr Miliband accused the PM of having a "hokey cokey weekend".
Three days, three positions. First it was no, then it was yes, then it was maybe.
Has there been a change in the Government's position, yes or no?
A nudge, nudge, wink, wink European policy is neither good for the country nor will it keep his party quiet.
David Cameron has risked angering Tory backbenchers by again refusing to back a quick poll on Britain's membership of the European Union.
The PM said he did not believe that voting to leave the EU would be the best thing for the country.
The right path for Britain is this. First, recognise that in the short term the priority for Europe is to deal with the instability and chaos.
Second, over time take the opportunities for Britain to shape its relationship with Europe in ways that advance our national interest in free trade, open markets and co-operation.
Third, all party leaders will have to address this question.
But it follows from my argument that far from ruling out a referendum for the future as a fresh deal in Europe becomes clear, we should consider how best to get the full consent of the British people.
Foreign Secretary Hague said there would be a "very, very powerful" case for a referendum if Europe moved towards a more federal system.Read the full story ›