Sandi Chen, who ran a brothel in New Malden that was raided and closed in 2002, blamed her sister Nikki Chen for the tip-off to police, a jury at Croydon Crown Court was told on Wednesday, April 28.

PC Graham Marr, of the Metropolitan Police’s human exploitation and organised crime squad, said Mr Dalton had spoken of revenge on his girlfriend Nikki Chen, after they fell out in December 2001.

He tipped police off at a meeting in the car park of Roehampton Hospital.

But PC Marr insisted Mr Dalton’s information was only one aspect of Operation Horsley, which saw madam and former hooker Monporn Hughes, known as Par, sentenced to three-and-a-half-years’ prison in 2003 for deceiving hundreds of women into sexual slavery in a chain of brothels.

When Mr Dalton contacted Surrey Police in six telephone calls and one meeting in August 2007, he told them information about Ms Chen.

He also handed over bank details, phone numbers and addresses for ringleaders of what he claimed was a network, based in Bayswater, that forced trafficked women from Thailand to earn up to £28,000 to pay off their debts.

But PC Jonathan Saville, in charge of covert human intelligence for the force, said although they had listened to Mr Dalton’s information and passed it on to the Met, he was not registered as a source and was specifically warned he should not commit a crime or risk his own safety.