Two men were yesterday jailed for life for murdering a fellow gangster they thought had become a "grass" after being caught with 14kg of heroin.

David King, 32, was hit by five of a burst of 26 bullets fired from an AK-47 assault rifle as he emerged from the Physical Limit gym in Hoddesdon in Hertfordshire in October 2003.

It is thought that the drive-by shooting by a masked man in a stolen Peugeot van was the first time an automatic weapon had been fired in a crime in Britain, let alone used to kill.

Yesterday, the gunman, Roger Vincent, 33, of Penn in Buckinghamshire, was told he would serve a life sentence of at least 30 years after he was unanimously convicted of murder at Luton crown court.

His driver, David Smith, also 33, from Elstree in Hertfordshire, was sentenced to a minimum of 25 years.

Jailing the pair, Mr Justice Wilkie said: "This was a thoroughly planned, ruthless and brutally executed assassination ... it was only by great fortune no other passersby were seriously injured or worse."

A third defendant, Julian Elfes, 38, of High Wycombe, Buckinghamshire, was jailed for five years for helping Vincent lie low after the shooting.

A fourth, Jason Attridge, of Harrow in north London, was cleared of murder.

The trial lasted seven weeks, and followed a Hertfordshire police investigation which tracked more than 100,000 mobile phone calls and took 1,200 witness statements. Officers were able to trace the defendants' movements in the days before the shooting, and to catch them discussing the attack over the phone.

Outside court, Detective Inspector Paul Maghie said the success of his team's "painstaking" investigation was down to "old fashioned detective skills".

The court was told that King, who lived with his partner and their two children in Stevenage, Hertfordshire, had been charged, but later released, when a 14kg (30lb) shipment of heroin was intercepted by customs officers - causing rumours among his criminal associates that he had become a police informer.

A contract was taken out.

The first gunman, Dean Spencer, 31, had lost his nerve when he saw King's sheer size, the court heard. He has since pleaded guilty to conspiracy to murder, and will be sentenced later.

Two weeks later, Vincent and Smith killed King as he came out of the Hoddesdon gym early in the morning; King's friend, Ian Crocker, who was with him in the gym, was also shot and injured.

He later gave evidence in Vincent's defence.

Det Insp Maghie said of King's killing with the Kalashnikov AK-47: "Clearly he was a criminal - but he had children, he had a wife and family, and we wanted justice for them.

"This is the first time that weapon was used in Britain in automatic mode - thankfully, by the grace of God no one else was injured."

The officer sought to reassure the residents of Hoddesdon, a small market town within the capital's affluent commuter belt, that there was unlikely to be a recurrence of the dramatic shooting: "Dave King was in Hoddesdon, that is why the weapon was taken there. There is no other link."