Nine illegal immigrants vanished after police put them on a train to a detention centre 80 miles away, a force said.
Officers gave the Afghan men tickets to travel from Cambridge to an immigration base in Croydon after they entered the country on a lorry, police said.
They were found on February 5 at a depot in Fordham, Cambridgeshire.
Cambridgeshire police said officers acted on advice from immigration officials in giving the men tickets to travel unaccompanied from Cambridge to Croydon.
Detective Inspector Alan Savile said: "In matters of this nature, the police are led by the UK Immigration Service, which in turns follows the Home Office instruction.
"In this instance the Immigration Service in St Ives was consulted and the decision taken to direct individuals to the immigration facility at Croydon, which is accepted practice."
But the Border and Immigration Agency (BIA) denied that police were acting on its guidance.
"It is not true that the BIA advised the police to tell illegal immigrants in Cambridgeshire to make their own way to Croydon," said a spokeswoman.
The spokeswoman added: "The police were advised to arrest them and hold them in custody so immigration officers could interview the subjects and hold them in detention.
"The police advised they could not take nine subjects into custody. Never at any point did the immigration officers advise the police to put the immigrants on a train to Croydon."
