The findings will be influenced by the new Migration Impacts Forum (MIF), which meets for the first time on Thursday to discuss the effects migrants have had on public services such as the NHS and housing.

Current rules limit the number of visas which can be handed to new arrivals from the two former Communist states.

Immigrants from Romania and Bulgaria - which joined the EU in January - can work here only if they fall into one of five categories. These are highly-skilled workers, students, those with specialist skills which cannot be met by resident labour, the self-employed and a quota of 20,000 low-skilled workers for the food processing and agriculture sectors.

Documents published by the Home Office showed the MIF will consider a report on "emerging findings" about the two new EU members in September, with a decision by ministers following some time in the final three months of this year.

Figures published last month showed nearly 8,000 Bulgarians and Romanians came to work in Britain in the first three months of this year, plus 2,400 who joined the seasonal agricultural workers' scheme. But the data did not provide a full picture of the numbers because no such records are kept by the Government.

At the end of last year Migrationwatch, which campaigns against mass immigration, predicted there could be 180,000 arrivals in the first year, while left-wing think-tank the Institute for Public Policy Research (IPPR) put the figure at 56,000.

The MIF will also influence the working of the new points-based immigration system. Each potential immigrant will be awarded points based on earning power, qualifications and other factors such as the demand for their skills in the UK job market. The MIF will be able to influence the "pass mark" and affect whether it is raised or lowered, depending on conditions in the UK.

Immigration minister Liam Byrne said: "We are creating the machinery for a much more open debate about where we need migration and where we don't but based on evidence, not anecdote. It is important that we involve and understand the experience of people from the front line - from local authorities, the health sector and businesses."

Shadow immigration minister Damian Green said: "This is all very well but, unless the Government adopts our policy of having an explicit annual limit on economic migration, this will be just another example of tough talk not matched by effective action."