Police have arrested 11 people after a raid on a suspected rip-off garage which allegedly held cars to ransom, with staff intimidating and even assaulting customers.
Bray Engineering in Southall, west London, attracted business from all over the country by advertising on the internet with extremely low prices.
But customers who complained when additional payments were taken off their credit cards were allegedly threatened, while the garage refused to return their vehicles.
Some have said it took months or years to get their cars back, with one van owner waiting two years.
One customer who booked in to have his engine reconstituted said he checked the engine number and found it had been replaced with a model from the 1970s.
A typical quote of £1,900 for work would allegedly often be doubled.
The garage, which featured in a recent Sky News investigation and has operated under several different names from 169 Brent Road, is run by Paul Dockerill and his sons, Martin and Harry.
About 75 officers carried out simultaneous raids at the garage and two home addresses.
Paul Dockerill, 45, and his son Martin, 23, both from Guildford, who were at the garage, were arrested on suspicion of conspiracy to commit fraud and assault.
Detective Chief Superintendent Andy Rowell, Ealing Borough Commander, said 30 complaints had been made against the garage from around the country already this year.
He said: "The allegations we have been investigating include threats of violence, intimidation and assault.
"What we have here is bad business treading the fine line between civil dispute and criminality. We suggest they've crossed that line.
"The level of complaints we have been receiving about this premises had to be acted upon."
Police said it was one of the worst alleged cases of a garage defrauding customers that they had come across.
About 29 people were working at the garage when police from the territorial support group descended in six vehicles.
Officers rushed into the premises where men in overalls were working.
Two men were arrested on suspicion of conspiracy to commit fraud, three on suspicion of assault, three over immigration offences and one over immigration and driving offences.
The raid also involved officers from Trading Standards, the UK Border Agency and the Department for Work and Pensions.