Since the abolition of embarkation controls, which started in 1994, no Government have ever been able to produce an accurate figure for the number of people who are in the country illegally and that includes those that might be working illegally.
By the end of December 2008, the majority of foreign nationals will be counted in and out of the country.
This is one part of the biggest shake-up of border security and the immigration system in a generation which also includes the global roll-out of fingerprint visas, compulsory watch-list checks for all travellers from high-risk countries before they land in Britain and ID cards for foreign nationals.
The UK Border Agency is committed to tackling illegal migrant working and will act on any intelligence it receives that a business is employing illegal workers. Equally, if an employer is found to be employing an illegal migrant worker and they have not ensured that the person has full entitlement to work in the UK, then they may be subject to a civil penalty of up to £10,000 or, in more serious cases, criminal prosecution. If convicted on indictment, the employer may face an unlimited fine and in some cases, imprisonment for up to two years.