A number of Britain's newspapers predicted on Sunday that Prime Minister Tony Blair would made a decision next week to do a U-turn on holding a referendum on the new European Union constitution.

The predictions were made after Blair declined repeatedly to rule out a poll.

In an interview with BBC Radio 4's Today program this weekend, Blair said "the thing that has changed recently is a radical change in the (opposition) Conservative position, which is no longer to say they don't support this constitutional treaty, but they would re-negotiate it if it was passed."

Asked if that meant there would now be a referendum, he said: "You will have to wait and see what occurs on any of this," said the prime minister who has previously rejected holding a referendum on the treaty.

In a report of the interview, The Sunday Telegraph newspaper claimed approval for the referendum will be sought from Blair's Cabinet on Thursday.

"Tony has crossed the line. It's now really a question of timing," the paper quoted a senior Cabinet minister as saying.

The Independent on Sunday also said a decision on a referendum would be made next week because Blair wants a "clear position" on the issue before the start of campaigns for the local and European elections.

It said that Blair was urged to "clear the air" by one of a band of his cabinet ministers promoting what they claim would be a tactical masterstroke.

"Every time we try to do anything on Europe we are accused of betrayal. We must clear the air. It is time to front these people up," the cabinet minister was quoted as telling The Independent on Sunday.

Previously Blair had insisted that voters would not be given a say on the controversial treaty due to be finalized in June, because the convention will not bring about "fundamental change".

Reports said his change came after the Conservative Party planned to make their demand for a referendum a key part of their European elections campaign.

But Blair has been warned not to "play games with voters over the issue by the Conservatives".

"If the government performs a total U-turn and holds a straightforward referendum...we will welcome that," said Michael Ancram, the Conservative Party's shadow foreign secretary.

"If they try and play games with the British people, the British people will see through them...(the conservatives) are against the constitution," Ancram said.