There is a complex range of economic, social and policy factors that will influence levels of labour migration. The National Institute of Economic and Social Research published the results of research into the economic determinants of migration to the UK2003:
http://www.niesr.ac.uk/pubs/dps/dp216.pdf
They found that a number of factors influenced legal migration flows including UK incomes relative to other EU countries and to source countries, the existing stock of immigrants in the UK and UK unemployment. The research does not cover asylum seekers, currently being considered. I refer my hon. Friend to the answer given on 30 November 2009, Official Report, column 486W.
In addition to economic factors, the points-based system, which was rolled out over the course of 2008, is an important means of controlling migration for the purposes of work or study. In response to recent reports from the independent Migration Advisory Committee, we will be adjusting the thresholds that determine the points allocated to prospective entrants, and have reviewed the shortage occupation list, to ensure that our policy truly reflects the needs of the United Kingdom.