A gang that smuggled into the UK the largest haul of assault rifles and submachine guns ever detected by police are facing life in prison after being convicted at the Old Bailey. The group brought the weapons into Britain via France by hiding them in a motor cruiser which docked in Kent last August. The haul included 22 AK-47-type weapons, nine submachine guns, more than 1,000 rounds of ammunition, two silencers and 58 magazines. Some of the weaponry was bought from the same Slovakian gun store that was the source of firearms used in the terrorist attacks on the offices of Charlie Hebdo and the Hyper Cacher kosher supermarket in Paris in January 2015.

Harry Shilling, 25, Michael Defraine, 30, and their associates were caught after armed police swooped on the Albernina when it docked at Cuxton marina, near Rochester.

Shilling and Defraine were on Thursday found guilty of possession of firearms with intent to endanger life and conspiring to import firearms into Britain. The judge told them they face possible life imprisonment.

Jennifer Arthy, 42 and John Smale, 58, were found not guilty. Three other members of the gang have already pleaded guilty to their part in the plot.

Officers from the National Crime Agency, which led the investigation into the smuggling, breached the PGP (pretty good privacy) encryption software installed on multiple BlackBerry phones used by the group to intercept messages as the trafficking took place. The UK is only the third country in the world, after Canada and the Netherlands, to have publicly said its law enforcers have been able to breach the PGP programme for encrypting data.

The NCA’s head of specialist operations, Rob Lewin, said: “This seizure of automatic weapons was the largest ever made by the NCA – and, we believe, the largest ever on the UK mainland. These are hugely powerful firearms…

“The evidence pointed to them (the gang) not being afraid to use guns themselves to expand their influence. They wanted to move up in the criminal world from regional to international gangsters.”

Bought as deactivated weapons in Slovakia for as little as £38 each, the firearms were illegally reactivated somewhere in Europe and the gang hoped to make £250,000 by selling them.

British police fear some of the guns could have got into terrorist hands via the known overlap between criminals and extremists. Tariq Hassane, who was convicted last month of conspiring to kill on the streets of London, was part of a cell which sourced a firearm, silencer and ammunition through a London criminal contact.

Duncan Atkinson, prosecuting, told the central criminal court in London that the firearms smuggled into the UK by Shilling and the gang were capable of causing carnage on a terrifying scale.

Prosecutors likened Shilling, who claimed he was a farmer specialising in rare breeds, to the fictional underworld boss Keyser Söze from the film The Usual Suspects.

Defraine arranged the transportation, while Shilling’s “loyal lieutenant” Richard Rye, 24, acted as a gobetween with those who would do the legwork needed to bring in the guns.

The weapons were shipped in from Boulogne, northern France, via the river Medway. But the group were being watched by National Crime Agency officers, who had been monitoring their activity for months.

Shilling sent one message following what he thought was the successful purchase and transfer of the weapons, which read: “We now officially gangsters.” To which his associate replied: “Fucking nice one.”

Armed police moved in to make the arrests on 11 August shortly after the weapons were transferred from the boat to a Renault van. They arrested Payne in the van on a dirt track near the marina. When arrested he was asked what was in the van, and replied: “Guns.”

After the arrests the deputy director of the NCA, Graham Gardner, said: “This was an extremely significant seizure, the largest of its kind in the UK. I’ve no doubt that these weapons would have ended up in criminal hands and it goes without saying the risk they would have posed to the public.”

During the trial armed police were present inside the courtroom for the first time since Kenneth Noye faced trial in 2000 for murder. The gang were brought in and out of court each day in a police convoy with helicopters flying overhead and jurors were kept in isolation throughout the proceedings.