An off-duty policeman jumped into an open-top car and told the driver: "Follow that man."

The suspected shop thief fled out of sight but Detective Inspector Bill Warner, a former taxi driver, guessed where the suspect was headed.

Minutes later, Mr Warner leapt from the car and cornered the man.

He was helped by a Big Issue seller, a man dressed in black, a young woman and a female shop assistant.

Mr Warner, an ex-boxer, said: "The public response from everyone was fantastic.

"I could not believe how they dropped everything and joined in the chase."

Mr Warner, of Brighton and Hove CID, was with his girlfriend and her child in Western Road, Brighton, on Wednesday when he saw a security guard chasing the suspect.

A Mercedes Benz convertible was passing and Mr Warner leapt over the door into the passenger seat.

He said: "I jokingly told the driver 'I'm commandeering this vehicle' and asked him to follow the suspect.

"I'd done the knowledge of the city when I was a cabbie so I guessed the suspect would run to Market Street. Sure enough that's where we spotted him.

"I grabbed him and then a man all in black and a Big Issue seller who had been chasing him turned up.

"They were followed by a young woman and then a woman shop assistant.

"What I did was what I'm paid for but all these other people just took it upon themselves to help.

"It was as if they were saying, 'How dare you steal in our city? We're not letting you get away with it'.

"It was admirable and I want to thank them all. Without their help I don't think we would have caught him."

Stolen property was later recovered. A man has been charged.