No details have yet emerged about the person, who was apprehended in the Brixton area of London.

Ron Davies still faces further questioning himself by police over the events on Clapham Common that ended him having his car stolen at knife-point.

Detectives investigating the case on Wednesday arrested three people, who were later released on bail without charge.

The assembly will go ahead - but who will lead it?

Mr Davies has been out of contact since his decision on Tuesday to quit the cabinet.

He is believed to be staying with his wife at friends while he considers whether to give up his post as Labour's leader in Wales.

He has come under increasing pressure to step down from the job - thus abandoning his hope of becoming the first Welsh 'prime minister' when the new assembly is set up.

Opponents say if the incident in south London was serious enough to make him resign as Welsh secretary, it makes his hope of being first secretary unviable.

Support slipping

There are signs that support for his assembly position is slipping away among senior party figures in Wales.

David Morris, the Euro-MP for South Wales West, told BBC Radio 4's Today programme: "I don't think he has got much option except to go.

"I think now because of the rumours that are circulating, because it appears that he in fact hasn't got confidence in his own people to share with them what he has done, I believe he is losing sympathy."

Ron Davies is a novice Druid

Senior Labour backbencher Donald Anderson (Swansea East) expressed concern that the full details of what Mr Davies had done were still not known.

"He has told the prime minister certain facts. Whether those are the complete facts, we do not know," he told the programme.

Union backing

But Mr Davies still has the support of the union which sponsors him. Unison leader Derek Gregory told Today: "He's done a brilliant job as Secretary of State and has made a thousand decisions which have been excellent judgements.

"We have to allow him a couple of days to reflect. If he stays, the party will unite behind him. If he resigns, the party will have to elect a new leader.

"What happened on Clapham Common would not affect Ron Davies's ability to carry out his job."

Brixton police station

Mr Davies's car was stolen after he was engaged in conversation with a stranger after dark and met up with two of the man's friends. He insisted he was a victim of a crime but gave no more explanation as to why he resigned.

The three people arrested were taken to Brixton police station, but the case was later taken over by Scotland Yard. A spokesman said inquiries were ongoing.