British lawmakers have demanded an urgent inquiry today into claims that up to 250,000 Romanians and Bulgarians will flock to Britain after restrictions are lifted at the end of 2013.

The estimate was given by pressure group Migration Watch UK. Earlier, government officials including David Cameron and Nick Clegg refused to disclose the official civil service forecast.

The figure was being taken as a serious warning by MPs on the cross-party parliamentary Group on Balanced Migration, the London Evening Standard informs.

In a joint statement, co-chairs Frank Field and Nicholas Soames said: “Given Migration Watch UK’s excellent track record of forecasting the scale of immigration, the Cross Party Group on Balanced Migration calls on the Government to examine with urgency the impact of such numbers and how an influx  on such a scale could be properly managed.

“Such an examination must include reviewing the current rules around accessing the benefits system which need tightening so that only those that have been in the country for a substantial amount of time and have contributed through taxes would have entitlement.”

On Monday, UK Prime Minister David Cameron said that it is currently impossible to predict immigration levels from Bulgaria and Romania when access restrictions are lifted in December 2013.

Temporary curbs on Romanian and Bulgarian migration were imposed by the Labour government in 2005 to protect the UK labour market.

From next year, like other EU citizens, Bulgarians and Romanians gain the unrestricted right to live and work in the UK where currently, they require authorisation before taking a job.