Police have begun an internal investigation into why three illegal immigrants were allowed to walk free from a police station.
The men were found in the back of a lorry load of mushrooms that was delivered to the Asda depot in Kempston, Bedfordshire, last Sunday.
They were taken to Greyfriars Police Station in Bedford and the Border and Immigration Agency was informed.
The Agency asked the police to keep the men, but they were released in error.
'Disappointing'
A Bedfordshire Police spokesperson said: "There is now an ongoing investigation into the reasons why they were released."
The men were aged 25, 30 and 35, and were thought to be from Pakistan and Iraq.
Alistair Burt, MP for North East Bedfordshire said: "It's always disappointing when something like this happens and the police have admitted their mistake.
"If we had a policy to detain everyone without fail then the police wouldn't be in a position of asking whether or not people should be detained.
The Home Office said it was clamping down on illegal entry into the UK.