Ministers are looking at measures to curb immigration from Bulgaria and Romania when existing controls are lifted at the end of this year, Downing Street has confirmed.
David Cameron's official spokesman said the Prime Minister wants to prevent potential damage to the UK labour market from a fresh influx of migrants, but acknowledged that Britain will have to operate within European Union rules on the right to free movement.
Transitional arrangements in place since 2005, which limit the rights of 29 million Bulgarian and Romanian citizens to live and work in other EU states, will expire in December. Campaign group MigrationWatch has warned that as many as 250,000 could arrive in the UK over the next five years.
The Government is coming under growing pressure to publish its own estimate of the scale of expected immigration from the two newest EU states.
No official figure has been put on the anticipated number of arrivals - with ministers wary of repeating the situation when Poland joined the Union and much larger numbers than predicted came to the UK.
Mr Cameron's spokesman played down reports that the Government was planning an advertising campaign to deter would-be migrants by warning them of low-paid jobs and rainy weather.
But the spokesman confirmed that ministers were considering ideas which might prevent a surge in immigration.
"As you would expect, the Government is considering what options there may be and the process of looking into these and considering them is under way," said the spokesman.
"The issue here is around dealing with potential damage to the UK labour market and potential scope for curbing immigration to that end.
"We are in the process of considering what we may be able to do. Clearly, there is a European legal framework within which we have to operate."