Four men were jailed for between 15 years and life after being found guilty today of carrying out a £1.75m robbery in the first English criminal trial to be heard without a jury in 400 years.

John Twomey, 61, Peter Blake, 57, Glenn Cameron, 50, and Barry Hibberd, 43, were all convicted at the Old Bailey after the judge heard evidence that they were responsible for "a professionally planned and professionally executed" armed robbery at the Menzies warehouse at Heathrow airport in February 2004, in which one member of staff was shot at and attacked.

Blake was sentenced to life in prison with a minimum term of 10 years and nine months, Twomey got 20 years and six months; Hibberd 17 years and six months; and Cameron, 15 years.

Twomey, the leader of the gang, wiped away tears and waved to a woman who wept in the public gallery as he was taken down to begin his sentence.

The four were tried, convicted and sentenced by Mr Justice Treacy after the previous three armed robbery trials collapsed, the last two amid allegations that the jurors had been "compromised" or tampered with.

The total cost to the taxpayer of the aborted trials is estimated to be at least £25m – more than 14 times the amount stolen.

Wearing masks, fluorescent jackets and dark woollen hats the men were armed and had been tipped off by an insider to the fact that currency was being stored in the warehouse.

During the raid the four rounded up the Menzies staff, and the prosecution says Blake fired repeatedly at David Westwood, a member of staff, with a handgun. The robbery, which was set up using an inside man, was supposed to have netted the gang £10m. But they misread the airline manifest showing the number of bags in the warehouse and only made off with £1.75m – none of which has been recovered.

CCTV footage produced by the prosecution showed Twomey, Cameron and Hibberd arriving at a hotel near Heathrow shortly after the robbery carrying what the crown said were a holdall and a large plastic bag, which appeared to be stuffed with the stolen money.

Key to today's successful prosecution was evidence given by a supergrass. Menzies supervisor Darren Brockwell, 42, had been dreaming up the raid for months after discovering bags of currency were held in a vault inside the warehouse in 2003.

After being put in touch with Twomey's gang, Brockwell studied flight patterns for weeks to determine when the vault would be full.

But on the night of the robbery he misread flight documentation and believed £10m would be in the vault, rather than just £1.75m.

He was arrested at his mother's house in Woking, Surrey, shortly after the raid. In his Vauxhall Vectra were two drawn maps of the warehouse.

At first he denied any involvement, but following discussions between his solicitors and the police, Brockwell agreed to turn supergrass and reveal all about the robbery. He ended up giving evidence in all four trials.

In March 2007 he was given a reduced sentence of six years, having admitted conspiracy to rob, in recognition of the help given to the prosecution. He was released later the same year.

But Brockwell will spend the rest of his life living under an assumed identity and his former wife and two young children have been moved to a secret location and given new names.

When this fourth and final trial began in January all the defendants were initially on bail but Blake walked out of the court and disappeared for three days. He returned to apologise to the judge and was remanded in custody along with his co-defendants to await a verdict.

The "hallowed principle" of trial by jury was set aside by the court of appeal in June last year, in the first case using powers under the Criminal Justice Act 2003, but campaigners called the decision a dangerous precedent.

Evidence seen by appeal judges of alleged jury tampering was kept from the public and defence lawyers because of what senior prosecutors described as the "sensitivity" of the information.

This evidence has never been shown to the defendants – who deny all suggestions they attempted to influence a jury – or their lawyers.

Crown Prosecution Service lawyers have refused to reveal the information relating to jury tampering, saying "risks" still exist from the past.

But it is known that one of the earlier trials, in August 2007, collapsed after one juror refused to return to court. In a series of "emotional and irrational" telephone calls the juror told court officials that he felt "like a prisoner in the building and in the jury room". He was discharged, and for other legal reasons Judge Jeremy Roberts QC stopped the trial and discharged the rest of the jury.

In December 2008 Judge Roberts was again forced to discharge the jury after two jurors reported allegations of "nobbling". He described the incident as "serious attempts at jury tampering".

All four defendants were today found guilty of robbery and having a firearm with intent to commit robbery.

Blake was also found guilty of attempting to cause grievous bodily harm and possession of a firearm with intent to endanger life.

Hibberd was found not guilty of 13 charges of unrelated firearms offences concerning a cache of weapons at a lock-up garage in Uxbridge, west London.

They will be kept in custody while they await sentencing.