The foreign secretary has pledged that the government will "respect" the result of any referendum on the planned European Union constitution.

But, speaking on Sunday, Jack Straw declined to say whether a second referendum was ruled out.

 "It goes without saying that we will respect the view and opinion and power of the British people in a referendum," he told BBC1's Breakfast with Frost programme.

"If there is a referendum, the Act of Parliament establishing a referendum will make it very clear that the British people have the final say and they will do.

"What will happen after that, I am not going to speculate on because it depends on what parliament and the British people then want to happen."

Straw added that the government remained confident of getting a "very good deal for Britain" during talks on the constitution, and that as the negotiations continued "the British people will come round to support that deal".

Meanwhile, shadow foreign secretary Michael Ancram called on the government to make it clear there would be no second vote in the wake of a "no" vote.

"If there is a 'no' vote, then there is no constitution," he told Sky News.

"That has been recognised across the board. We would then be back where we are now.

"We would have to talk with our colleagues about where we move forward to from there."