The government underestimated the number of migrants from the EU

Tony Blair's official spokeswoman said a decision would be made "at the appropriate time" later this year.

The comments came after Trade Secretary Alistair Darling told the BBC there would be no "open door" to migrants.

The two countries could join the EU in January 2007. The Conservatives say the government should limit work rights.

When the EU expanded in 2004 the UK had been one of only three countries not to restrict work rights.

The government had expected up to 13,000 to come to work in the UK from the new EU members, such as Poland, but so far an estimated 600,000 have.

A fresh influx could "put unacceptable pressure on public services, on school places, on the provision of housing, which causes big problems for certain local communities", Tory immigration spokesman Damian Green warned at the weekend.

Seven years

Mr Darling, asked if there would be an open door policy, told the BBC on Sunday: "No. No one who deals with the immigration system fails to realise we have got to have a system that is properly managed, properly controlled."

That was interpreted as signalling that there would not be unchecked work rights for Romanians and Bulgarians.

But on Monday Downing Street denied that a decision to curb their work rights had been taken.

The spokeswoman said Mr Darling had been discussing the issue in general terms "talking of the general need for managed migration. In terms of Bulgaria and Romania, decisions on that will be made at the appropriate time".

The European Commission will issue a report on Bulgaria and Romania in the autumn, which will indicate whether they should join the EU on 1 January or whether there should be a delay.