There were no gunshots, kidnaps or car chases through London, it was instead a very understated escape. In the midst of a fourth criminal trial for a £1.75m armed robbery, Peter Blake walked unnoticed out of the door of the Royal Courts of Justice and failed to return.

Police and prosecuting sources privately voiced anger and frustration at the ease with which a man facing the first major criminal trial to take place without a jury in more than 400 years had gone on the run. Blake was one of four defendants charged over a robbery at Heathrow airport in 2004.

The sources pointed out that Blake's bail application had been opposed by the prosecution on the grounds that he might abscond and because of the serious nature of the offences.

Suspicions were first raised when Blake did not appear in the dock after the lunch break on Wednesday. When he failed to show up again yesterday morning it became clear he might not be returning.

Detective superintendent Stuart Cundy, of the Flying Squad, said yesterday that an all ports alert had been issued and police were actively hunting Blake, 57, whom he described as dangerous. "We would ask members of the public not to approach Peter Blake, but if they do see him to call 999 immediately," said Cundy.

The raid for which Blake is standing trial took place in February 2004 when six men arrived at a Heathrow warehouse in the back of a security van. They were wearing identical masks, black woolly hats and fluorescent jackets and had been tipped off by an insider to the arrival of a huge haul of foreign currency from Austria.

Sixteen members of staff were tied up as the armed gang raided the vault before fleeing the airport site in what has been described as a 'professionally planned and professionally executed' inside job.

The crown alleges that Blake fired at one of the warehousemen, David Westwood, and then struggled with him, discharging his handgun again.

The prosecution case is that Blake's DNA was found on a balaclava and mask which was pulled from one of the robbers' heads.

Blake states that he was at his terminally ill mother's home on the night of the raid, later visiting his sister to give her a birthday card.

He states his DNA matched that on the clothing because he was approached to join the gang during a meeting at the home of Chris McCormack, a known enforcer for the north London criminal gang, the Adams family.

Too scared to upset McCormack he said he tried the outfits on during the meeting. 'There was a bag of hats, masks and reflective coats," he has told the court. "I tried the clothing on because he [McCormack] told us to. I was thinking 'Jesus Christ what have I got myself in to'. I didn't want to lose face."

Blake's departure from court 35 of the high court is the latest in a string of costly setbacks to hit the investigation and prosecution of those responsible for an audacious, professional armed raid. The ongoing saga has included the use of a supergrass insider, the acquittal by jury of one team of suspected robbers, a key defendant suffering a heart attack at Belmarsh prison, a hung jury, repeated whispers from police and prosecution sources of jury tampering, and a criminal judge admitting that the case had left him devastated.

In the meantime no one – except the supergrass who pleaded guilty – has ever been convicted for the robbery at the John Menzies warehouse, the costs have soared to tens of millions of pounds, and the historic judge-only trial was granted by the court of appeal which ruled there was a serious risk of interference with any future jury.

At the opening last month Blake, who has previous convictions known to the court for armed robbery, and his co-defendants were all on conditional bail having put up sureties worth tens of thousands of pounds. On the first day they were pictured outside the high court, free to come and go during the proceedings having handed over their passports to the authorities as part of their bail conditions.

Blake, who lives in Notting Hill, west London, was only arrested in July 2005 – after the first criminal trial at the Old Bailey had failed to convict anyone of the heist.

The jury-less trial is continuing in Blake's absence.