Visa checks are being carried out on a man arrested on suspicion of working illegally as a guard at a 2012 Olympics sailing site in Dorset.
The man, a 26-year-old Pakistani national, was working full-time on a construction site at an Olympics development in Portland.
Dorset Police arrested the man on behalf of the UK Border Agency (UKBA).
The UKBA said the firm that employed the man faced a £10,000 fine if it was unable to prove it carried out checks.
The man had a student visa but this only allowed him to work 20 hours a week.
The UKBA said it would investigate a college he was meant to be studying at in Northamptonshire.
The college said the student had a 95% attendance rate, despite the fact he was apparently working full-time in Dorset.
The man is in detention and could face deportation.