William Dempsey, Barry Kelly, Craig Thomson Colquhoun and James Martin Ashdown were sentenced at Liverpool Crown Court yesterday for their part in the conspiracy, which was uncovered after a "befuddled" alcohol and drug-abusing soldier abandoned the weapons at a railway station.
Police said the reason why the weapons were headed to Scotland will remain a mystery, as the key men with the knowledge pleaded their innocence to the last.
Dempsey, 29, left two Army camouflage bags containing an Uzi sub-machine gun with silencer, a handgun and a sawn-off double-barrelled shotgun at Carlisle station as he stepped off the Glasgow-bound train.
The soldier, then a mortarman with the 5th Battalion, Royal Regiment of Scotland, was dressed in desert combat uniform when, exhibiting "somewhat bizarre behaviour", he told rail staff he was being followed by police and there were snipers at the station.
Dempsey, from Paisley, had collected the firearms from his friend, Ashdown, 32, in Canterbury, Kent, and they were destined for underworld figure Kelly, 34, and his "lieutenant", Colquhoun, 28.
Kelly, of Dalquhorn Avenue, Darvel, and Colquhoun, of Murray Place, Barrhead, were jailed for nine years and seven years respectively after they were found guilty by a jury earlier this month of the same firearms offences.
Dempsey, of Woodhead Gardens, and Ashdown, of no fixed address, were each jailed for eight years at Liverpool Crown Court after pleading guilty at earlier hearings to conspiracy to buy or sell illegal firearms. Drug addict Ashdown received an additional three years for possession and intent to supply cocaine in a separate case.
Sentencing the four, Judge Robert Warnock said: "I am wholly satisfied that [the weapons] were destined for use in serious crime and had a clear potential for causing serious injury and death.
"Had these firearms reached their intended recipients, I have no doubt they would have significantly contributed to the upward spiral of gun crime in this country."
A British Transport Police (BTP) spokesman said: "Kelly and Colquhoun are the key to knowing what was going to happen to those guns. Dempsey and Ashdown were literally just supplying them, and as far as we know, they had no idea.
"Both Kelly and Colquhoun still protest their innocence, so it's very difficult to get any information about where the guns were going in Scotland."
Detective Chief Inspector Simon Taylor, who led the BTP's investigation, said: "These four clearly intended to put illegal firearms on to the streets of Scotland and it is a fair assumption that they would have been used to commit criminal acts or to intimidate people.
"In uncovering and unravelling the complex conspiracy, BTP, in partnership with Kent Police and Police Scotland, have taken this potential threat out of circulation and ensured the conviction of four dangerous men."
The court heard that on August 17 last year Dempsey left his identification papers and 194 rounds of ammunition in the bags, which had his name embroidered on them. He had a final pint in a local pub before he was arrested.
Officers subsequently arrested Kelly, Ashdown and Colquhoun and during the arrests found £20,000 hidden in Kelly's house. Mobile phones were also seized, and analysis of these cemented the links between the four men.