The treatment of detainees at Haslar has been criticised

The move comes after the centres - in Dover, Kent, and Haslar, Hampshire - were criticised by prisons inspectors.

Operating procedures were called into question after it was found detainees were being treated like prisoners.

Over the next 18 months, operational control will pass to the Immigration and Nationality Directorate (IND).

Immigration minister Des Browne said: "Detainees have always been held under the rules of removal centres rather than prisons.

"But it is an anomalous situation and the Prison Service and IND have been working together for several months to consider the various options."

Prisons minister Paul Goggins said the decision would "allow the Prison Service to focus fully on its core business of managing convicted offenders and remand prisoners under its custody."

'Happy birthday' sang

The Prison Service and IND will also discuss ways of improving service standards at a third centre in Lindholme, South Yorkshire.

Lindholme has been criticised by prisons inspectors previously for its poor translation facilities after staff at the centre sang Happy Birthday to a detainee who could not speak English in a bid to establish his date of birth.

Haslar was also deemed "unfit" last year after prisons inspectors criticised staff for carrying out strip-searches regardless of whether there were grounds for suspicion.

A security review was launched at the Dover centre last October after the escape of 24 detainees in seven months.