Gavan, a bus driver from West Yorkshire, manufactured highly dangerous firearms and explosives at the home where he lived with his mother.
Police discovered 54 improvised explosive devices including nail bombs and a booby-trapped cigarette packet at the address in Batley, as well as 12 firearms.
He added: "You had in 2007 joined the BNP, and written in your own notebooks indicating strong hostility towards immigrants in this country."
Although Gavan, who told the Old Bailey he had "a fascination with things that go bang", did not have a clear target for his weaponry police found a list of names, addresses and personal details of four people at his home, including that of a woman who had featured on a documentary on the July 7 bombings as a neighbour of one of the bombers.
Gavan, 38, is listed as having "gold" membership of the BNP and a copy of its magazine Hope and Glory were found at his home.
One hand-written notebook from his home contained the slogan: "The patriot must always be ready to defend his country against enemies and their governments."
Gavan pleaded guilty to 22 counts including collecting information useful for terrorism and possessing explosives and firearms.
Detective Chief Superintendent David Buxton, Head of the North East Counter Terrorism Unit, said: Gavan was an extremely dangerous and unpredictable individual.
"The sheer volume of homemade firearms and grenades found in his bedroom exposed his obsession with weapons and explosives.
"However, he was not simply a harmless enthusiast. Gavan used his extensive knowledge to manufacture and accumulate devices capable of causing significant injury or harm. As such, he posed a very clear risk to public safety.
"Our investigation revealed Gavans violent potential and while he had no single cause or agenda, he represented no less of a threat to our communities."
In addition, police found a copy of the Yellow Pages that had been fired into and that air pellets had been fired into the wall. Gavan was also apparently in the process of making a rocket launcher.
Further explosive material included weedkiller and hydrogen peroxide.
A samurai sword, a crossbow and a stun gun as well as books and magazines about guns and the military, and a computer file of the Anarchists' Cookbook, described as a "how to" manual about anarchism and explosives were also found at his home.
Simon Darby, a spokesman for the BNP, said: "If people are going to build up large arsenals then they will get stiff sentences. It's the inevitable consequence of enforced multiculturalism. You are going to get more and more incidents like this. It sounds like this was a lucky escape."