The Government will have the "smallest margin possible" for wriggling out of a pledge to hold a referendum on significant EU treaty changes, Europe Minister David Lidington said today.

He was speaking as the Conservative-led coalition faces its first trial of strength with backbench Tory Eurosceptic MPs in the Commons today.

The EU Bill, which ministers say proclaims the sovereignty of the UK Parliament and guarantees no further transfer of significant powers to Brussels without a public poll, reaches its committee stage on the floor of the House.

Rebel Conservative MPs have tabled amendments they say toughen up the Bill because the existing measure gives ministers too much scope to bypass a referendum and could leave judges to rule on what law-changes would qualify.

Eurosceptic MP Peter Bone told the BBC Radio 4 Today programme: "A number of Conservative colleagues have put down amendments which will toughen it up and make it what the British people want.

"They want Parliament to be supreme. I hope the Government will accept some of the amendments that are laid down, but if they don't then some of us will vote against the Government's line."

Mr Lidington told the programme: "We are saying any future change to EU treaties, however minor, will be subject to a full Act of Parliament.

"Any extension of EU competencies, (such as) a decision like joining the euro, would have by law to go with a referendum. There would be no wriggle-room for the Government.

"And we have two clauses which make it clear that Parliament has the final say in deciding whether EU law has effect in the UK."

He dismissed the rebels' fears, saying: "The wriggle-room for ministers is narrowed down to the smallest margin possible."