Yarl's Wood Helpline

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A spokeswoman said: "We have got no information to suggest anyone was in there but it is a possibility.

"It is unlikely to be the case but until we have had a chance to look around we don't know."

Search efforts have been hampered by the intense heat and structural damage to the �100m complex near Bedford.

Firefighters damp down at the �100m centre

Separate inquiries by the Immigration Service, police and Group 4 are under way into the incident, which caused damage costing an estimated �38m.

Officers were attacked when an argument erupted in the visitors' centre on Thursday night and had their keys snatched.

Six people, including two police officers, were injured in the riot.

Design flaws

Immigration minister Lord Rooker, who has inspected the devastation, is to examine fire chiefs' concerns that design flaws helped the fire spread rapidly.

He said it was extraordinary no water sprinklers had been installed at Yarl's Wood, despite a fire brigade recommendation a year ago.

"This is the easiest country in the European Union in which to work illegally so we are stepping up our system to deal with failed asylum-seekers," he said.

The destruction of half the building leaves Home Secretary David Blunkett's asylum policy in serious trouble as many of the residents will have to be housed elsewhere.

Built last year to house 900 people, Yarl's Wood is Europe's largest immigration centre.

Group Four said 123 detainees have been transferred to other sites, with 222 remaining in the undamaged area.