The Union and all around me people are rising in a standing ovation. Small wonder, really; Hill’s story is a compelling one.

Lured into the ranks of the National Front in 1960s Leicester, Hill soaked up the anti-Semitic literature his mentors bombarded him with. Yet from the late 1970s until the early 1980s Hill acted as a mole first in the South African National Front, then in the British Movement here in the UK. In 1984, Hill openly took part in a Channel 4 documentary investigating the true face of British Fascism; his subsequent experiences were proof of the terror which he had exposed.

Twenty minutes after his Union appearance, Hill and I are sitting in a room in Cambridge’s Jewish Centre. I had not been one of those who stood at the end of Hill’s speech; perhaps because I had more time to question him, and wanted to draw my own conclusions on the man, mostly because I wanted to get to the bottom of how he had pulled himself out of an all-consuming ideology and pledged himself so wholeheartedly against it. With difficulty, I was to learn.

First things first: Hill cautions against confusing activists with leaders, and voters with activists. “There is nothing more dangerous in this country than a strong, intelligent white working-class lad with no education, no prospects and no hope in life!” he had declared at the Union.

The raison d’être of Hill’s campaign against fascism is to resolve the disconnection between the ‘liberal elite’ (apparently made up of our governors) and the white working-classes on whom the fascists rely for votes. Those on the centre-right have often said that the government’s dismissal of objections raised against immigration has contributed to the rise of the BNP. I ask Hill if he thinks this is true: “Almost certainly. My politics are generally slightly left of centre but I think the government’s immigration policy has been irresponsible.

“I got involved [in Fascism] for the best possible motive; I wasn’t motivated by hatred but by poverty and frustration. However I think I was becoming twisted, I was halfway there! My wife recognised it and I recognised that she was right so I was very fortunate. If I hadn’t been married to who I was married to I might have got in too deep to have been able to pull myself out. That never happened; I was never 100% in there, they never had me – thank god!”

And yet those in the Movement who courted Hill were wealthy and educated. Indeed his most important mentor, Colin Jordan, was a Sidney Sussex alumnus. What motivated these guys? “That is the $64,000 question! I just do not know; there is no excuse for it. [Jordan] went to Cambridge. He was a very clever man, a capable speaker, a good organiser... such a sad waste, somewhere along the line the guy got twisted, and it could have happened to me. He had the opportunity to pull himself out of it like I did and he chose not to do so.... these people made their choices. [They] will probably always exist. The best we can hope for is to cut off their life-blood, and their life-blood is the frustrated white working class.”

In 1969 Hill, entrenched in poverty, moved to South Africa to become a miner. Several years of political inactivity followed until in the late 1970s Hill was encouraged by some Jewish friends to infiltrate the South African National Front and pass on information. I ask Hill how he could switch from being a far-right die-hard to becoming a Fascist saboteur: “There was a long period in South Africa when I was completely uninvolved in politics,” he answers, “but I was unfulfilled. I guess if I’ve made a mistake I try to put it right, and I had made a monumental mistake.”

The role gave rise to conflicted feelings, Hill describes meeting an Indian family squatting on the roadside after being evicted by the South African police: “This reinforced my already established hatred of fascism, but also made me do a bit of soul searching. You can’t make an omelette without breaking eggs. And I had to make contributions to the National Front, and perhaps part of the contributions I’d made led to these poor bastards being where they were. To that extent it was a very traumatic event.”

Hill returned to Leicester in 1979 and rejoined the British Movement. This time, though, he was under the auspices of Searchlight, an anti-fascist magazine for whom he collected information. In 1981 he uncovered an alleged bomb plot on the Notting Hill Carnival: “I found out about the bomb plot in Paris. I actually got one of the guys on tape implicating himself in the plot; I went into a bar with a recorder on my briefcase and he blurted it all out. I’d got him! But of course that isn’t acceptable as evidence. It wasn’t sufficient to get him nicked but it was sufficient to prevent the plot being carried out.”

The plot is evidence, Hill claims, of the “intrinsically violent, terrorist” nature of British fascism. His experiences after his 1984 exposé add weight to the claim. “After the programme for Channel 4 was made we had to move, but they found us after about a year. One night some guys crept round and left a gas canister with a blowtorch propped against it outside my son’s bedroom – if it had went off nobody in the room would have survived.”

More than just thuggery, then. I ask him how high up the Fascist hierarchy he believed these threats were being sanctioned: “High. I was getting phone calls saying ‘we’ll get you, you bastard.’ They said they would bring boys over from Italy to do it. We had to leave.”

Our thirty minutes is almost up and I only have time for one more question. This man has stared in the face of fascist terror, he knows more than most about what’s at stake – I ask him if he thinks political censorship is an acceptable tool to fight fascism. He responds thoughtfully: “I think we’ve reached the stage where we have to be very distinct in what we mean by censorship. I support wholeheartedly the no-platform-for-fascists policy that most universities have.

“I can’t stop them renting the room in a building around the corner from me to spread this poison if they want to, but I don’t have to let them into my front room. So what I shall concentrate on doing is to encourage all decent organisations, all decent pub managers, all decent breweries and controllers of any buildings which could possibly be used for that purpose to simply not give them that platform. I don’t consider that censorship I just consider it the exercise of my individual freedom.”

A fair point. This man is full of fair points – in my experience the Union has never hosted a speaker who has so frankly and openly washed away the preconceptions of the audience. You can’t help but be taken aback by the conviction with which he expounds the case against fascism, a conviction honed not just out of his own experiences inside the BNP, but out of his underprivileged background in the kind of community upon which the BNP depends. The next time Nick Griffin is on Question Time, let Jack Straw stay in Westminster and put Ray Hill on the panel instead.