I am the sort of person I suppose who lets people use the toilet when they say they are desperate

Oliver Letwin Shadow home secretary

The thief reappeared holding Mr Letwin's wallet and ran through the open door.

Speaking to reporters during a visit to Brixton Prison, Mr Letwin said his "human instinct" in allowing the conman into his home had been "misguided".

He said: "The man said he was desperate to use the toilet and I am the sort of person I suppose who lets people use the toilet when they say they are desperate to use one."

The shadow home secretary denied reports he chased the thieves down the street and grabbed his wallet back.

'Angry tone'

Mr Letwin, who was preparing for a business trip to Amsterdam, maintained he only followed them out of the front door and shouted at them.

"It was not at all dramatic. I merely shouted at him 'stop' and 'give me my credit cards back'."

Asked why he thought the cards had been returned, he said: "I haven't the slightest idea, maybe they were simply very surprised to hear someone saying something ostensibly so ridiculous in such an extremely angry tone of voice."

Mr Letwin later realised the thieves had escaped with his electronic organiser, mobile phone and some of his wife's jewellery.

Con trick

Asked if he had learned a lesson from the incident, he said: "What we say about crime in central London is absolutely true, as if I didn't know that already."

He added: "Being the subject of a con trick is no fun for anybody but it makes me more determined than ever to tackle crime in this country."

A spokesman for the Metropolitan Police said: "Police were called at to reports of a theft at an address in Kennington."

The spokesman told BBC News Online an investigation was being carried out by Lambeth Burglary Squad.

He reiterated the force's advice for victims of theft to call police rather than pursue the culprits.

Rising star

Oliver Letwin is considered to be one of the rising stars of the Conservative Party, with a strong Thatcherite background.

Within a year of entering parliament in 1997, he was appointed party spokesman on constitutional affairs and was later promoted to shadow chief secretary to the Treasury.

In the general election campaign in 2001 he hit the headlines with comments suggesting the Conservatives would be able to cut taxes by �20bn rather than the official �8bn figure.

But that does not appear to have hurt his career prospects and he became shadow home secretary after Iain Duncan Smith's election to the Tory leadership.