A member of the notorious gang that tried to rob the Millennium Dome in London is back behind bars after being jailed today for 13 years for a bungled security depot ram raid.

Raymond Betson was one of six would-be robbers who, dressed in black boiler suits and wielding baseball bats, targeted Loomis UK on an industrial estate in Mark Way, Swanley, in the early hours of March 23, 2012.

But Maidstone Crown Court heard the raid failed and the gang fled empty-handed when a digger smashed into a loading bay instead of a cash vault containing more than £1 million.

The gang, who also used the digger to rip a hole in a fence to make their escape, had to abandon their getaway vehicle, a stolen Mitsubishi Warrior 4x4 bearing cloned number plates, in a nearby field when it got stuck in the ground.

Betson, 52, formerly from Chatham but now of Clifton Crescent, Folkestone, was the only member to be arrested.

Forensic tests on a balaclava and snood found in the 4x4 revealed a DNA profile matching the married father.

But Betson, who represented himself at his trial in July, denied attempted robbery and claimed he had only worn the headgear while paintballing.

The jury of nine women and three men were told of his previous conviction in 2002 for conspiracy to commit robbery at the Dome, where there was an exhibition of £200 million worth of diamonds.

Betson drove a JCB used in that raid, and at today's sentencing hearing for the Loomis raid Judge Charles Macdonald QC said there was an "extremely strong" inference that he was driving the digger.

The judge, who described the raid as "professionally planned" added: "You were one of six men in a gang who carried out reconnaissance over a number of days."

Betson sat in the secure dock flanked by three prison officers after an application for him to be handcuffed was refused by the judge.

He acknowledged relatives and friends sitting in the public gallery when he appeared by raising a hand clutching legal documents, and simply nodded to them once he had been sentenced and was led back to the cells.

Betson claimed during his trial he was a reformed character and the court heard of his work with a debt charity.

At one stage he conceded he did not have a "cast iron" alibi, but asked the jury: "Can you be sure I was not in bed?"

After being found guilty by a 11-1 majority, Judge Macdonald advised Betsonto appoint a legal team for the sentencing hearing.

Today, defence counsel Jonas Milner said the largest aggravating feature of the case was Betson's involvement in the Millenium Dome raid in 2000, for which he was jailed for 18 years, later reduced to 15 years on appeal.

However, Mr Milner added that the Swanley raid "lacked ruthlessness" and involved neither firearms nor violence.

"There is no evidence of a leading role or that of a ringleader," he said, "but he cannot be said to be a subordinate or foot soldier. There is simply an absence of evidence."

Mr Milner also told the court that there was another side to him "at odds" with his convictions and that a lengthy sentence would have a "crushing" effect on his partner and son, who suffers from ADHD.

At the start of the Loomis depot trial, prosecutor Christopher May told the court that staff were loading a van at the depot at about 5am when they heard what sounded like an explosion. They then saw the bucket of the digger sticking through the wall.

The "robbery of the Millennium" also involved the raiders crashing into the Dome.

They were carrying a nail gun, ammonia, smoke grenades and sledgehammers and planned to escape in a speedboat.

But they were arrested by armed police within minutes. Had it succeeded, it would have been the biggest robbery in UK history.