The £1.75 million Heathrow robbery trial was abandoned for the third time at the Old Bailey today, at a cost to the public of £22m.

John Twomey, 60, the alleged robber, will now face a fourth trial over the hold-up of Menzies World Cargo warehouse at the airport in February 2004 after Judge Jeremy Roberts discharged the jury after five months.

Judge Roberts would not give any reason for the decision, which he said left him "devastated" and which he added came despite the "enormous cost to the public".

"I don’t quite know how to say this, because it is the last thing I wanted to tell, you but I am afraid we are not going to be able to continue with this trial," he said.

"In the course of a major criminal trial like this one, events sometimes occur which create the risk of real injustice or unfairness to one side or the other and sometimes those events are so serious that the trial cannot continue.

"That is what has happened in this case. It wouldn’t be appropriate for me to give you any further information about what has occurred."

Jurors looked stunned as the judge informed them of his decision and excused them from serving again for 10 years, while one woman member of the panel shook her head angrily as she walked from the courtroom.

The judge added: "Everybody is devastated by the fact this has happened. I have tried everything to avoid this conclusion and I very much regret that it has been necessary to take this action."

During the airport raid, six masked men rounded up members of staff at gunpoint and stole £1.75 million in an alleged "inside job", the court has heard.

Mr Twomey first faced trial in 2005 when proceedings against him were stopped for health reasons.

He then faced a fresh trial, which began in February last year and lasted six months, alongside co-accused Peter Blake and Barry Hibberd, but jurors were unable to reach a verdict.

Mr Twomey faced the charges for a third time in the dock of the Old Bailey in July this year, this time with a fourth defendant, Glen Cameron, alongside him.

All four are due to appear at the court next week for a hearing to set a date for a fourth trial.

Mr Twomey, of South Avenue, New Milton, Hants; Mr Blake, 56, of Colville Houses, Notting Hill, west London; Mr Hibberd, 42, Goldhawk Road, Shepherd’s Bush, west London; and Mr Cameron, 49, of Kenilworth Road, New Milton, were bailed.

They deny charges including conspiracy to rob and to possess firearms.

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