Prime Minister David Cameron is facing renewed pressure over the European Union after he tried and failed to satisfy Conservative demands for a referendum.
This morning, the former defence secretary Liam Fox said for Britain should leave the EU unless the terms of the country's membership can be renegotiated.
In his first major speech since resigning from the Cabinet last year amid allegations over inappropriate links to a lobbyist, Mr Fox warned that Britain's national interest is at risk as the Government's power is "curtailed by diktat from Brussels".
In a speech at an event organised by The Taxpayer' Alliance, Mr Fox, a well-known eurosceptic, said:
Mr Fox also said he would like to see Britain "negotiate a new relationship with the EU based on economic rather than political considerations, and set out in clear and unambiguous language".
But he stressed: "If this approach is rejected outright or falls short of our necessary red lines then we would have no alternative but to recommend rejection and consider departure from the European Union.
Liberal Democrat MEP, Sir Graham Watson, described Liam Fox's speech as "a desperate move by a discredited Tory to bang the populist drum to try to revitalise an ailing political career".
Later today, David Cameron will make a Commons statement on last week's EU summit.
Mr Cameron has said he is prepared to consider a referendum on the UK's EU relationship, but only when the time is right.
In an article for The Sunday Telegraph, Mr Cameron acknowledged the need to ensure the UK's position within an evolving EU has "the full-hearted support of the British people".
He stressed there would be further opportunities in the coming months and years to win back powers from Brussels and that he wanted to be able to offer voters a "real choice" in any potential referendum.
David Cameron's official spokesman has said that his position on a referendum does not represent a shift from his comments at the European Council last Friday, when he appeared to be ruling out a poll.
The spokesman told a daily media briefing in Westminster.
Meanwhile, some Conservative MPs warned that the Prime Minister had not gone far enough.
Tory MP John Baron, who organised a letter from Conservative backbenchers to Mr Cameron calling for a referendum after 2015, demanded a commitment from the Prime Minister.
Shadow foreign secretary Douglas Alexander branded David Cameron's possibility of an EU referendum as a sign of "weakness".
The leader of the UK Independence Party (Ukip), Nigel Farage said Britain is no closer to getting a referendum on the EU.
Speaking on BBC1's Sunday Politics Show, he said:
The Liberal Democrats said David Cameron was speaking as Conservative leader regarding an EU referendum, and not for the coalition as a whole.
A Liberal Democrats spokesman said: