Fears that an influx of Romanians and Bulgarians to Britain will put a strain on public services have been downplayed in an independent report published by the Foreign Office.
But the number that may arrive on UK shores after immigration restrictions are lifted next year remains unpredictable, according to the study by the National Institute of Economic and Social Research (NIESR).
Schools were likely to take much of the strain but the effect on the NHS, the housing sector and the welfare system will be less pronounced, it said.
Bulgaria and Romania joined the European Union in 2007 but under "transitional arrangements" workers from the two countries were prevented from travelling to the UK. According to a British Labour Force sample survey, there are currently 26,000 Bulgarians and 80,000 Romanians living in the UK, but the actual numbers could be larger, according to the report.
Last month, Communities Secretary Eric Pickles admitted the Government had "no idea" about the size of the possible influx. Yet to begin with at least, the impact on public services will be modest, with the strain only potentially increasing if Romanian and Bulgarian migrants choose to settle in the UK on a long-term basis.
Families migrating from the two countries could put pressure on primary school places and although migrant children do not bring school performance down, language assistance will need to be provided. But initially future migrants are likely to be young, low-skilled workers who do not have families, the report said. Because most migrants will be young - mainly under 35 - and healthy, they will have a minimal impact on the health service, it said.
The report said the effect on housing is highly dependent on whether migrants settle in the long term, but evidence from local surveys showed that Romanians and Bulgarians are interested in coming to the UK, but it is not a favoured destination and many are interested in temporary stays rather than long-term moves.
Romanian and Bulgarian migrants are likely to be low-skilled workers - employed in construction, catering, hospitality and as carers or cleaners, the report said. Currently, the main destinations for Romanian and Bulgarian migrants are Spain and Italy, and to a lesser extent Germany, the NIESR research found. Spain and Italy in particular are favoured because of similarities in language, and may continue to be favoured due to the presence of social and economic networks in those countries. But with the economic situation in southern European countries precarious, that may change.
Home Affairs Select Committee chairman Keith Vaz described the report as "helpful" but said it contained no estimates of expected arrivals. He added: "It would be helpful if Theresa May visited Romania and Bulgaria to gauge the reasons why their citizens would choose to migrate to the UK."
The minister for Europe, David Lidington, welcomed the report as a contribution to the debate on migration. "The report will help to shape this Government's work to build an immigration system which works in the national interest - supporting the UK economy by continuing to attract the brightest and the best global talent at the same time as protecting our public services and ensuring our welfare system is not open to abuse," he said. "Our tough new rules are already taking effect, with overall net migration falling by almost one third since 2010."