The Home Office has refused to state how many staff the Immigration Service has to deal with employer tip-offs about illegal workers.
Last week, controversy over the issue erupted, after a report by the Recruitment and Employment Confederation revealed that concerns raised by businesses were often ignored owing to a lack of resources.
The online survey of 432 recruitment agencies showed three-quarters had been given what they thought were fake documents by foreign staff. However, nearly half said the Immigration Service did not take action when they reported it.
A Home Office spokesman said: “While we always seek to remove those who have no right to be here, resources and operations always have to be prioritised to maximise the number of people we remove and for reasons of public protection.”