The Omagh bomb, the Lithuanian sting and the Real IRA plot to bomb the mainland

Republican Michael Campbell was yesterday jailed after trying to buy an arsenal in the Baltics to wage terror in Britain. Kim Sengupta lifts the lid on the MI5 operation that brought him down

"You imagine us getting over to England, if you had 10 of them and 10 clocks in a holdall. You imagine, with a six-hour timer we could be over to London and back. Just tick, tick, tick, tick... Gone. Leave it anywhere."

Michael Campbell was setting out his plans for carrying the Real IRA's bombing campaign to the heart of the enemy in the British mainland.

The senior member of the dissident republican organisation – whose brother Liam Campbell was found liable in a civil court case of responsibility for the Omagh bombing – was celebrating a coup which would bring grenades, Kalashnikovs and snipers' rifles, into their arsenal for a devastating offensive and open up a channel for lethal supplies in the future.

But the 39-year-old had been caught in a MI5 sting. Yesterday he was convicted in Lithuania of attempted smuggling, attempting to aid a terrorist organisation and illegal possession of weapons – and jailed for 12 years. The security forces regard the conviction as a milestone in the continuing battle against splinter groups waging sporadic terrorist campaigns.

Campbell was taken to Lithuania by an MI5 agent. The arms dealers carrying out negotiations worked for the intelligence service. The operation, law agencies claim, prevented attacks which could have led to dozens of deaths. Others back in Ireland are wanted over the alleged plot. Lithuanian authorities are seeking the extradition of Liam Campbell, described as the former Quartermaster-General of the Real IRA who, along with its leader Michael McKevitt, was held to be behind the Omagh atrocity in a case brought by some of the bereaved families of 29 people who died in the August 1998 bombing. A warrant has also been issued against Brendan McGuigan, another senior alleged member of the group, who travelled to Lithuania with Michael Campbell.

The mission was one of the most complex and longest carried out by the Security Services against Irish paramilitaries. It saw the unprecedented appearance of an MI5 spy, Robert Michael Jardine, in the witness box in open court. The Lithuanian judicial system did not allow for the the protection of a screen, the usual practice in the UK. Campbell's defence team repeatedly charged that Jardine was an agent provocateur who had lured an unsuspecting Campbell at the behest of MI5 to incarceration in a foreign land.

MI5 and Lithuania deny entrapment. The Real IRA, they maintain, instigated the purchase of arms and saw Jardine as a useful conduit; the Campbell brothers and McGuigan were seasoned terrorists and it is risible to portray them as innocents led astray.

Mr Jardine voluntarily decided to give evidence and must now start a new life with a false identity. "He will have to live the rest of his life looking over his shoulders," said one security official. "He is not overtly political. He did what he did to prevent loss of lives. The trial would not have proceeded without his evidence. He was given the choice whether to give evidence and he chose to do so."

In 2002 Mr Jardine, who is in his mid-40s and of an English background, smuggled cigarettes to boost his legitimate earnings. In that role he met Kevin Tumelty, who was involved in dissident Republican circles. This also brought him to the attention of MI5, investigating terrorist funding. An approach took place and Mr Jardine agreed to help.

Tumelty died but in July 2004 an associate of his, who had struck up a friendship with Mr Jardine, asked him if his contacts could supply weapons. The MI5 agent handed over a price list for items, written, for "authenticity", in the Cyrillic alphabet. He also introduced his contact, named Tomas, a member of the Lithuanian intelligence service. The deal appeared to stall but in 2006 Mr Jardine was approached by Campbell and met other Real IRA members.

The paramilitaries had suspicions. Mr Jardine was told: "We know MI5 are coming for us. You better not be one of them."

A particularly menacing incident made Mr Jardine think his double life had been exposed. He was told he would be taken to meet Real IRA leaders, but entering the back of a transit van he found it covered in plastic with a shovel on the floor – the props of a traitor's last journey. The traitor would dig his own grave then be shot. The plastic covering was to avoid forensic evidence. "This was an act of cold-blooded courage, that is not a cliche, it's a fact," said an official familiar with the mission. "I wouldn't have blamed him if he pulled out."

The fact that Mr Jardine had not panicked and attempted to escape raised his credibility with the Real IRA. Doubts were assuaged.

In August 2007, Campbell, calling himself "Freddie", and another Real IRA operative, "Shaun", travelled to Lithuania to stay with Tomas. Mr Jardine had insisted negotiations should take place between the two parties directly, to try to avoid subsequent accusations of entrapment.

Three days later the two visitors were introduced to another "arms dealer", who they named "Rambo". The three men went to the woods to practice with weapons including rocket-propelled grenades.

Satisfied, they left a deposit of €5,000. The Real IRA men seemed to think they were getting a bargain. In a whispered conversation, secretly recorded, Campbell struggles to hide his excitement: "Look at it this way, for one of them and one of them you have a bomb... for a fucking hundred quid!"

The two men returned to Ireland. Next month Campbell met Rambo in Marbella to work out future transactions. As well as having the weapons, the Lithuanian was told, the Irish wanted training on how to use them.

On 21 January 2008, Campbell travelled to Vilnius with his wife. The following day Rambo took the Real IRA man to a garage to show the arms cache available. It is there, in grainy video footage and crackling audio recording, that Campbell, according to prosecutors, incriminated himself. Examining detonators and timers for bombs, he muses, pointing, "See them there now... they would be good for under a car." Rambo: "For what?"Campbell: "Booby trapping a car... anchored to a wheel and then the car goes around... Bang!"

The Barrett sniper's rifle was of particular interest to Campbell and he was set to pay €1,000 (£869) for one to be shipped over. Rambo asked if something so potent would be used for merely hunting "roe deer" or "wild boar". Campbell said, "No, no we will be shooting from across the border." Rambo asked: "Who will be the targets?" Campbell said: "Brits."

But Rambo still had to pin down exactly who Campbell represented. "I don't need any matters with criminals. It is very important to me," Rambo said. Campbell tried to reassure him: "Criminals do not need that type of training." He needed the gun, he said, for his "enemies". He was asked for his identity or, at least, to give the name of his organisation to the man who would deliver the Barratt. Campbell said he belonged to the "IRA".

Campbell was tackled by soldiers from Lithuanian special forces as he left the garage. In court he insisted that Mr Jardine was the man driving the arms purchase. He himself was "just joking" when he talked about using the weapons against British targets, planting bombs in London. "To make something so big out of a joke was really unfair."

Secret lives the informants

Robert Michael Jardine may have been denied the protection of a screen as he gave evidence in a Lithuanian court house, but even that would not have hidden his face from the memories of the men who will feel he betrayed them. He will have a new name, new documentation, a new home, and, in so far as is possible, a new appearance.

There may be people out to get him, but they are fewer in number, resources and organisational capability than those charged with his protection. The Real IRA is a splinter group with no more than a couple of hundred members. They lack the intelligence networks and the contacts the Provisional IRA once had, and they are not active in England.

In the past, IRA informants were recruited locally. When exposed they tended to disappear, placed secretly in England or Scotland.

One such, Martin McGartland, was recruited by the Royal Ulster Constabulary but his cover was blown in 1991 and he was abducted by the IRA. He escaped execution by jumping from a third-floor window. He was eventually given £100,000 and resettled in Whitley Bay, Tyne and Wear. In 1997, he was caught speeding and his identity inadvertently exposed by Northumbria Police. Two years later he was shot six times, but recovered from the injuries. He was relocated immediately, protected by 12 armed officers and given an armoured car.