At least 14,000 registered asylum seekers have gone missing in Britain and many are believed to be working in hotels and restaurants, the Government admitted last week.
The Government said that the missing thousands have breached their temporary agreements and cannot be traced.
Pressure groups are calling for an amnesty, but the Home Office is relying on its tracking unit, set up two years ago, to seek out the absconders and their employers.
"Very often they are working in the catering trade," said a spokesman from the Home Office. "We know there tend to be plenty of jobs available in the catering industry. We get information from a variety of sources and if we believe people are working in a hotel or restaurant we will go in there."
Martin Couchman, deputy chief executive of the British Hospitality Association, agreed that as many as 10,000 illegal immigrants could be working in London's hotels and restaurants, probably in small businesses. "Large employers in London tend to have very efficient personnel systems," he said. "Smaller employers are less inclined to check."
But Jane Sunley, managing director of recruitment agency Mayday, argued that the black market in false documents makes it extremely easy for illegal immigrants to deceive any employer.
l Eight labourers working on the building of a five-star hotel in Cardiff Bay for RF Hotels were arrested last week following a joint operation between police and immigration officials.
Four were found to be legitimate asylum-seekers while the other four received detention orders. No action was taken against the subcontractor.
By Christina Golding