Sion Aubrey Roberts, 21, of Llangefni, Anglesey, was convicted earlier this month at Caernarfon Crown Court of possessing explosives and sending explosives with intent to endanger life.
The court heard how Roberts, a machine operator, sent devices to a Welsh Office minister, Sir Wyn Roberts, a Tory agent, Elwyn Jones and two senior police officers.
Two other men accused with him were acquitted. All three denied the charges. Roberts claimed he had been framed by police and MI5 officers involved in the investigation.
Mr Justice Pill, sentencing Roberts, said that what he did was 'nasty and brutish and can't be dressed up in any other way. It must be demonstrated that squalid activities such as this can't be tolerated'.
Judge Pill said in December 1991, four alarm clocks and substantial quantities of a homemade explosive mixture had been found in a bedroom at Robert's home. The clocks had been modified for use in devices.
The mixture was dangerous and Roberts intended to endanger life or cause serious damage to property. Devices which were intercepted in the post were likely to cause serious burns and put at risk postal workers and others, he said.
Nigel Mylne QC, for Roberts, said his client was unlikely to have masterminded the arson attacks. Outside the court, Roberts's mother Einir Roberts said her son and two other accused were not members of Meibion Glyndwr but belonged to a group called The Covenantors, a legal organisation seeking Welsh independence by 2000.
'It's not Meibion Glyndwr or the IRA. The police haven't caught Meibion Glyndwr and I hope they never will. Why are the police so obsessed with them - they're not killing anybody?' she said.
During the eight-week trial MI5 agents who gave evidence hidden behind screens admitted they twice broke into Roberts's flat to plant bugging devices.
Detectives filmed Roberts wearing protective clothing as he handled explosives. They also filmed bright flashes which they said were caused by him testing the devices.
Roberts told police he sympathised with Meibion Glyndwr. He admitted taking part in an IRA-style colour party complete with black berets and armbands at a memorial parade to commemorate two Welsh nationalist 'martyrs' who died when the bomb they were carrying blew up in 1969.
The Chief Constable of North Wales, David Owen, said yesterday that despite the 'many wild and irresponsible allegations' made against investigating officers 'not a shred of evidence was adduced in support.
'The jury rightly convicted Sion Aubrey Roberts. The case was properly brought and the investigating officers acted correctly throughout,' he said.
'Bombs are made with the sole intention of killing or maiming and recent events give graphic evidence of this. Sympathy and support for people who behave in such a manner is ill-conceived and eventually is the road to anarchy.'Reuse content