Vincent Wood, 29, a sales executive from east London, who admitted republican sympathies but said he opposed violence, showed no emotion when the jury found him guilty of possessing explosives with intent to endanger life. The unanimous verdict came on the sixth day of his trial.
In the witness box, Wood, bespectacled and smartly dressed, claimed he had been tricked by his Irish brother-in-law, Gerard Loughney, into looking after a tea chest containing 17.5kg (38lbs) of Semtex and five timing units. Only detonators and batteries would have been needed to create bombs.
The prosecution told the jury that the issue was not whether he possessed the explosives, but the purpose for which they were being kept. Sentencing, Mr Justice Ognall said he was entirely satisified that since Wood's marriage to an Irish nurse and through meeting her family, he had 'initially supported and then actively espoused the terrorist cause'.
As an intelligent man who had led a respectable life, Wood made 'an ideal vehicle' for the safekeeping of explosives. The judge added: 'And when the summons came . . . you would have provided them to the bombers with potentially terrible consequences, and those consequences would have embraced political assassination.'
When detectives raided Wood's home in Leytonstone, they discovered recently burnt fragments of a street plan of the area surrounding Mr Major's constituency home at Great Stukeley, near Huntingdon.
The main fragment recovered was a thumbnail-sized piece with the boundaries of the house clearly marked; the figure six was written on it, believed to be a reference to the fact that the house is six-tenths of a mile from a roundabout.
A senior counter-terrorism source said last night it was believed the IRA was actively plotting to bomb Mr Major's home: 'This had gone further than the idea stage. We were looking at what must have been a serious attempt on the life of John Major.'
But police found no other evidence of the Major plot. Neither was it clear whether Wood had 'minded' earlier shipments of explosives.
Wood is believed to have been 'sounded-out' and then approached by the IRA when on family trips to Ireland. The source stressed that his conviction underlined the fact that the IRA was actively seeking recruits from non-Irish backgrounds; it was likely similar people were in place.
Detectives are concerned that Wood was apparently tipped off by the IRA in a telephone call to his office that he was under surveillance, allowing him to rush home and destroy the map. Surveillance techniques are believed to have been revised.
Wood denied being a member of the IRA but admitted the lesser charge of unlawful possession of explosives; a charge of conspiracy to cause explosions was dropped.
He told the court that after discovering the contents of the tea chest, he and his wife, Maraid, were shocked but afraid to go to the police. He eventually left it at the shop of Tony Robinson in Goodmayes, Essex. It was opened by a curious colleague of Mr Robinson's, who became suspicious and notified police; the Woods were put under surveillance.
Although Roman Catholic and of Irish descent on his mother's side, Wood was brought up in London as an Englishman. He became politically active, supporting left-wing causes and took an interest in Irish affairs. He met his wife, a psychiatric nursing sister, at Gaelic classes in London.
The court heard that she came from a subsistence farming family in Co Mayo with no political affiliations. Mrs Wood was not in court yesterday; Mr Wood's parents were said to have been 'shattered' by the verdict.