Two men jailed for armed robbery have been freed following a corruption investigation into Scotland Yard detectives.

The pair say officers from Scotland Yard's elite Flying Squad had planted a gun on them when they were arrested. John Woodruff, 63, and William Hickson, 56, were jailed for 17 years for conspiracy to rob, robbery and having firearms at the Old Bailey in April 1997.

Although they had been due to face a retrial, a judge has now ruled that their case was "permeated by the stench of police corruption" and a new hearing would be unfair.

The men say their claim is backed by evidence of police wrongdoing uncovered by the BBC.

The case centres on the alleged robbery of a post office in Manor Park, east London, in 1996.

Flying Squad officers lay in wait for Woodruff and Hickson. But the pair, both from east London, said at their trial they had been set up by the police. They said they had been lured there after being told that cash would be given to them across the counter.

The officers who arrested them were later suspended during a crackdown on corruption. The BBC's Nine O'Clock News found evidence, on a video tape, supporting their claim that a gun had been planted on them.

The film shows the tape appears to have been cut - as the timer jumps - and a gun appears during the gap.

Mr Woodruff and Mr Hickson appealed, and their convictions for armed robbery were quashed last November. The case was then referred back to the Old Bailey for a retrial.

At the new hearing, Judge Geoffrey Grigson allowed a defence submission that it would be an abuse of process to try the men again. He said a fair trial would be impossible and it would be wrong to go ahead.

He said 12 officers in the case were tainted so the men should be freed.

Mr Hickson said: "I was set up by the police for a robbery that wasn't a robbery. There are a lot of corrupt police out there and it's still going on. I had a gun planted on me."

This is the latest in a series of cases to be overturned since a crackdown on police corruption began in 1998.

Two veteran criminals given a retrial on robbery charges because of concerns about alleged corruption among Flying Squad officers were cleared at the Old Bailey yesterday when the new hearing collapsed.

Judge Geoffrey Grigson, who was to preside over the retrial, threw out the charges after hearing that the Crown wanted to proceed without the officers, who are now facing corruption charges or disciplinary investigations.

The prosecution had not wanted to call the officers, including the detective in charge, but to rely on a statement about investigations into them. Judge Geoffrey Grigson ruled that John Woodruff, 63, and William Hickson, 56, both from east London, could not have a fair trial if the Crown produced only a "sanitised" version of the facts.

Woodruff and Hickson, who both had substantial criminal records, were jailed for 17 years in 1997 for conspiracy to rob, robbery and possessing firearms following an armed raid at an east London post office in 1996.

The pair were said to have stolen two parcels containing £32,500 in cash. They claimed that evidence against them was fabricated and they were granted a retrial last year after the Appeal Court heard about investigations into Flying Squad officers.

Two armed robbers, nicknamed "Mad Dog" and "Chainsaw Woody", walked free from court yesterday after a judge ruled they could not have a fair trial because of the involvement of allegedly corrupt Scotland Yard officers in the case.

John Woodruff, 63, and William Hickson, 56, had been accused of taking part in the robbery of £33,000 from a post office in Manor Park, east London, in January 1996, armed with a handgun and a bottle of ammonia. They were jailed for 15 years each in 1997 for the crime but the Court of Appeal ordered a retrial into the case after the officer who investigated their case was arrested on corruption allegations. The defendants claimed weapons had been planted on them.

Their case is one of the first to be overturned because of allegations that trials involving officers accused of wrong-doing in the Metropolitan Police's anti-corruption drive are now tainted. Dozens of convictions are being challenged after the corruption purge at the Yard.

At the Old Bailey yesterday, Judge Grigson cleared the men of conspiracy to rob. He said: "It is my judgement that no fair trial is possible. Serious allegations were made against 25 members of the squad, including the officer in charge ... of the operation involving these defendants."

"Mad Dog" Hickson and "Chainsaw Woody" Woodruff, both from east London, have been sentenced in total to 60 years in prison for a series of multi-million-pound robberies. In the Sixties Woodruff was jailed for 12 years for armed robberies with sawn-off shotguns. He was jailed again in 1979 for 18 years for his part in a robbery in Banstead, Surrey, in which an armed gang waylaid a security van, cut into it with a chainsaw and stole more than £1m.

Hickson was arrested after the £6m robbery on a Security Express depot in 1983. Accused of handling cash from the robbery, he was jailed for six years and then went to ground.