At a press conference at 10 Downing Street after a meeting with Prime Minister Gordon Brown, Mr Barroso said he had every reason to believe that the treaty opt-outs sought by Britain would be kept in the text.

Mr Farage said: "That is not true and he knows it. The treaty is now set in stone. Britain's much vaunted 'red lines' are so much dust. He knows this and is merely trying to bolster Gordon Brown's massive deception on the British people."

Mr Brown told the press conference that failure to achieve the "red lines" would mean that Britain could not accept the treaty.

But Mr Farage dismissed this assurance. "Mr Brown knows that he won his seat promising a referendum," he said. "Mr Barroso knows it and, what is more, every man, woman and child in our country knows it.

"Anything less than a referendum would be a dereliction of duty."

Opt-Out may not be option

Commission Vice-President Margot Wallstrom today admitted that the British opt-out on the Charter of Fundamental Rights was not "set in stone", despite claims by the government that the red lines decided before European Summit had not been breached.

UK Independence Party leader Nigel Farage said: "The fact that the European Commission itself does not seem to think that Britain's opt out on the Charter of Fundamental Rights holds water just makes it clear how weak the Government's position is.

"The Prime Minister has suggested that we can have a referendum if his precious red lines are crossed. The Commission has just rubbed one out. We need a referendum on the Treaty".