From Oxford University: http://www.migrationobservatory.ox.ac.uk/resources/briefings...
Does immigration create greater unemployment or greater inactivity among existing workers? The first systematic study of this issue used data for 1983-2000 to analyse how changes in the share of migrants impact on employment, labour market participation and unemployment of existing workers (Dustmann, Fabbri and Preston 2005). It concluded that immigration had no statistically significant effect on the overall employment outcomes of UK-born workers. The study did, however, find statistically significant effects on specific educational groups of UK-born workers: immigration was found to have adverse effects on employment, labour market participation and unemployment of UK-born with intermediate education (defined as O-level and equivalent) and a positive impact on employment outcomes of UK-born workers with advanced education (A-levels or university degrees).
A separate study carried out by researchers at the Department of Work and Pensions (DWP) analysed the impact of labour immigration of A8 workers on claimant unemployment during May 2004-November 2005 (Lemos and Portes 2008). The study found little evidence of an adverse effect. There is some evidence to suggest that, just like the impact on wages, the effects of immigration on unemployment differ between the short and long run. An OECD study of the impact of immigration on the unemployment of domestic workers in OECD countries (including the UK) during 1984-2004 found that an increase in the share of migrants in the labour force increases unemployment for those with skills most similar to the migrants in the short to medium term (over a period of 5-10 years), but that immigration has no significant impact on unemployment in the long run (Jean and Jimenez 2010).