British voters are likely to be given the opportunity to vote in a referendum on the planned European Union constitution, a move that would mark a major U-turn by the Labour government.
The EU constitution, yet to be finalised, is aimed at ensuring the smooth running of the bloc after it expands from 15 to 25 members in May. Once agreed, it has to be approved unanimously by the 15 existing members and 10 newcomers.
Prime Minister Tony Blair has so far resisted calls from the opposition Conservatives to put the issue before the public, arguing that ratification by parliament is sufficient.
Mr Blair's critics say he has refused a referendum because he fears a largely euro sceptic public would oppose it.
Speculation has grown following an interview on Saturday when Blair refused to rule out a referendum.
"Our policy has not changed and if there is any question of it changing, I can assure you we will tell you. You will have to wait and see," Mr Blair told BBC radio.
The BBC said it had learnt Mr Blair had now agreed to hold a referendum and an official announcement would be made this week, possibly after a cabinet meeting on Thursday.
Some observers say the Blair government could put a broad question to the public about overall support for Britain's role within the EU rather than pin it to a new constitution.
Others say the talk may be a tactic to take the steam out of the opposition's call for a referendum ahead of June's European elections when Mr Blair's Labour party is set to get a drubbing.
"It may well be that he has decided he has got to talk about having a referendum - we still don't know whether he means it," Conservative home affairs spokesman Mr David Davis said in a television interview.
EU leaders failed at a summit in December to approve a constitution when negotiations collapsed in a row over member states' voting powers, but they will try to agree by the end of June.