A London black cab driver convicted of sex attacks on 12 women may have targeted hundreds of victims, police believe.

John Worboys, 51, a former stripper who abused women in the back of his taxi after giving them spiked drinks, could be one of Britain’s most prolific sexual predators.

A total of 85 more women from London and Dorset have come forward since he was charged last year and officers believe there could be many more.

Police are now facing serious questions about why they arrested Worboys in June 2007 but then released him.

He is believed to have committed as many as 40 more attacks before he was arrested a again and finally charged eight months later.

The Independent Police Complaints Commission (Ipcc) has been called in to investigate why Worboys slipped though the net.

IPCC Commissioner for London Deborah Glass said: "It is clearly concerning that despite the Metropolitan Police arresting Worboys in the summer of 2007, he went on to attack a more women."

Since the Worboys case the Metropolitan Police has changed the way it investigates sex crimes. Control of the Sapphire Units - teams that deal with rape and sex assualt cases - have passed from the boroughs to the central Homicide and Serious Crime Command.

The court heard how Worboys targeted young professional women – including a solicitor, a journalist, an advertising executive and a hedge fund manager - who emerged from fashionable West End nightclubs between 1am and 3am.

Carrie Symonds, 20, of East Sheen, was one of Worboys’s youngest victims. In July 2007 he picked her up at a bus stop in King’s Road, Chelsea, promising to take her home for £5 “because he lived that way”.

Worboys told her he had won the lottery and offered her a glass of champagne. Worried that it was spiked, she poured it out on the taxi floor.

The cab driver then said a passenger recently performed a sex act on him for £350 and asked if she would do the same. She refused.

Seeing that the drink had no effect, he dared her to down a glass of vodka in exchange for £50 and a free cab ride home.

“I downed it, which was stupid, as I just wanted to get home. From that point on I can’t really remember what happened.”

What should have been a 30 minute ride took an hour and a half. When she finally arrived home in East Sheen, she was violently sick and collapsed in front of her mother.

"I feel that if I was assaulted I would instinctively know. That's what I hope."

His other victims, who cannot be named for legal reasons, include women from Putney, Balham, Fulham, Herne Hill, East Sheen, Feltham and Twickenham.

Police found a “rape tool kit” in the boot of Worboys’s Fait Punto, consisting of two types of sedative drugs, a box of condoms, a vibrator, wine, Jack Daniel’s, whisky, vodka, small bottles of Tesco champagne and wine glasses.

Before becoming a taxi driver, Worboys, who lived in a £520,000 riverside home in Bermondsey, south east London, worked as a male stripper under the name "Terry the Minder". Using the aliases "Paul" and "Dave", he also directed and appeared in a porn film.

On Friday at Croydon Crown Court Worboys was found guilty of 19 charges against 12 women – including one rape, five sexual assaults, one attempted assault and 12 charges of drugging passengers.

Worboys denied all the offences and was cleared of two drugging charges.

Trial judge Mr Justice Penry-Davey adjourned sentencing until 21 April. He told Worboys to expect a "very substantial term of imprisonment".

Outside court, Det Insp Dave Reid, of the Metropolitan Police, said: "There may be some women who have had experience of Mr Worboys who have not yet reported that matter to the police.

"I would ask any women who have anything to report to us that they do so."

Police have opened a special phone line - on 0800 121 4441 - for women to call if they believe they may have fallen prey to Worboys.