Karl Cronin, thought responsible for defrauding Fulham and Chelsea landlords of more than £5million, is being hunted by police after appearing on Crimewatch last night.

An episode of the BBC programme launched an appeal to trace well-spoken playboy Karl Cronin, 42, who police believe is responsible for 15 property frauds, the majority of which took place in Kensington and Chelsea, Fulham and Putney.

Cronin, who may have used up to 11 aliases, targeted estate agents by claiming to be the owner of rented properties on which the mortgage had been fully paid. He remorgaged the properties, took the cash and left the rightful owner with the bill.

Until April 2008, he lived in Cornwall Gardens, South Kensington, but he has also lived in Fulham. Police say he has travelled widely but may still be in west London.

"He's travelled the world living in all the best hotels. He has gambled all over Kensington and Chelsea in casinos. He's a playboy," said officer on the case Det Con Leon Munday, of Kensington and Chelsea CID.

Police are hoping that west London estate agents who may have dealt with Cronin come forward with information to help them trace the fraudster.

Cronin has previously used the names Karl Lacey Cronin, James Maw, Jonathan Carson, Derek Moule, Andrew Moore, William Frederick Biles, David Aldam, Alan Garcia, Andrew James Tapper, Karl Keynes or Karl Lorenzo(COR).

He is white, 5ft 9in, of a medium build with short brown hair. He has a tanned complexion and his English is well spoken. Anyone with information is urged to call Kensington and Chelsea CID on 020 8246 9210. If you wish to remain anonymous call Crimestoppers on 0800 555 111.