"Stitch us up, and we'll fuck you over badly," the voice growled. It belonged to a fat, leering face, the mouth set in a small, intimidating 'o'. Sour breath wafted over me. Paul David 'Charlie' Sargent was a leader not so much by charisma as by force and fear. Around him a clamour of guttural "yeahs" supported his words.

The time was autumn 1996. Unknown to my friends, family or partner, I had arranged a meeting with the leadership of Combat 18, Britain's most notorious neo-Nazi gang. The '1' and '8' in their name stands for the initials 'A' and 'H' in the alphabet, those of Adolf Hitler. I'd contacted anti-fascist magazine Searchlight and they'd suggested I write a story about the gang and its desire for an "Aryan homeland" in Essex. I was to be the first outsider to meet them.

Combat 18 had garnered a fearsome reputation for its violence and links to Loyalist paramilitaries. As we sat smoking and drinking in an oddly respectable pub in Holborn, central London, terror suddenly gripped me. What the hell was I doing here? I was beginning to regret my initial enthusiasm for a story. I gulped and sought to hide my growing disquiet as the pub chatter carried on around us.

It was here in a pub surrounded by drinking commuters that I was introduced to a tribal world of maleness and violence, where ideologies of hate and extremism operate across frontiers. I had begun a journey that would change my life.

My travels would bring me to places where the boundaries with my own beliefs sometimes blurred. Where 'respectable' folk could be racists; where I swapped gossip about beer prices and TV programmes with men who could squirt acid into the face of an Asian woman, then laugh about it. This is the world to which Charlie introduced me. He was at the raw, elemental end of it. Most of the time, though, I discovered that hate wears a different face altogether.

In this world, I found extremists of all shades mixing together: fascists with vegans, animal liberation extremists with anti-abortionists, and a mêlée of small far-left, anarchist, far-right and environmental groups on the fringes of the anti-capitalist crusades. Not all these groups had fascist tendencies but many were led by zealots. In the USA, the notorious neo-Nazi National Alliance has set up an anti-globalisation movement. In fact, most of the people I interviewed were anti-capitalist and anti-globalisation. I also encountered the ultra-Catholic and neo-fascist International Third Position, which had spun off vegan groups and animal rights organisations, as well as anti-abortion pressure groups.

During my six-year journey, millions of my fellow Europeans - people who loved their children, worked nine to five, and thought of themselves as respectable citizens - voted for neo-Nazi and ultra-nationalist parties.

Which was my world and which theirs? I often couldn't tell. It was fear that drove them. I sensed it all around me, a cancer that seeped into our lives, allowing us to do terrible things. In the wings, lurking behind the smiles and smooth talk of the racist politicians, I discovered the pale faces of the boy-next-door killers, barely men, burning with frustration, needing belief, prepared to act. Loners and zealots like London nailbomber David Copeland, or Oklahoma bomber Timothy McVeigh.

Something was at work here. My travels inside Britain's subcultures had led me to the 'outsiders', those rejecting or placing themselves outside society. I encountered the likes of Charlie Sargent, Scandinavian neo-Nazi gangs prepared to kill police and British National Party leader Nick Griffin.

I even lived with the BNP's man in America, before being unmasked in a hotel in North Carolina by members of the world's most notorious neo-Nazi cult, the National Alliance. Before his death last year, the Alliance was run by neo-Nazi ideologue, William Pierce. His book, The Turner Diaries, about a worldwide racist uprising, was found in the possession of the Oklahoma bomber and in the flat of David Copeland. My encounter with Pierce's number two man was extremely unpleasant, but thankfully short-lived.

Deep in the mountains of Arkansas, I visited fundamentalist, racist Christians. I was called undercover to Beirut for a conference of Holocaust deniers and Islamic fundamentalists. Later in my voyage, I crossed paths with Europe's smiling ultra-nationalist politicians. And at the end of this strange odyssey of mine, I gained exclusive access inside the "liberated zones" rising in the former East Germany, where a founding member of the Baader-Meinhof gang was helping to lead a neo-Nazi political party.

Everywhere I looked, and turned, hate seemed to surround me. The people I met were all searching for something: belonging, power, a second of meaning or glory in their lonely and frightening world. But I did not simply want to parrot that "the Fash" were a bunch of leather fetishists with deep Oedipus complexes and an unhealthy interest in homosexuality.

There was a definite undertone of homophobia among almost all far right movements I met, and there is a common view that all fascists are sexually repressed. Many certainly were. Yet there are many other real reasons and causes - the failures of the left and social democracy for a start - that suggest why people were voting for the right. Still, I could not help but be struck by the sheer number of angry, intense and deeply repressed individuals flocking to this scene.

It's at this point the cry goes up from the right that you meet similar characters on the left, and that this is the nature of politics and power. The same sort of 'lone wolf loony' excuse is used to support the notion that the British National Party or National Socialist Movement (a tiny neo-Nazi group spawned by Combat 18) had no responsibility for or influence on the London nailbomber, David Copeland, who'd belonged to both groups. But so-called 'lone wolves' are undoubtedly attracted to, and influenced by, fundamentalist groups. These groups add to the momentum that helps tip potential killers over the edge (they could just as easily end up in a cult, a far left group, a protest movement - anything as long as it's fundamentalist). Yet every right-wing leader I met tried to deny they bore any responsibility for some nut actually taking them at their word - i.e. start a race war. You don't see Copeland, or Buford Furrow (a white supremacist who shot Jewish children in a kindergarten in LA), Maxime Brunerie (the French neo-Nazi who tried to assassinate French president Jacques Chirac on Bastille Day) or Thomas Nakaba (a Danish member of C18, a bomber whom I followed in my travels) in mainstream political parties. You find them on the fringe.

What I discovered - or had affirmed - during the research for my book, Homeland, was that I was witnessing the distorted face of belief. There were people, whether neo-Nazi skins or leaders of xenophobic political movements, who wanted to contain our often complex and confusing world with a black-and-white straitjacket.

Why? Fear, insecurity, the pace of change, perhaps. The changing shape of communities and work patterns: the downside of economic globalisation, something that unites a disparate network of groups from right to left. Identity seems key, too. Particularly male identity. It was hard to find women actively involved in these groups. There were some, particularly in the ultra-nationalist Vlaams Blok (Flemish Block) in northern Belgium, which now accounts for 10 per cent of Belgium's MPs and one third of the vote in Antwerp, and in the Austrian Freedom Party - but even here they are always outnumbered by men.

In the subcultural groups, whether a British hooligan gang or a German kameradschaft, ('comradeship') the identity I discovered seemed more tribal, rebellious, perhaps a brotherhood to replace loss of traditional community and family. A loose-alliance of extreme right social networks, the kameradschaft have declared swathes of former east Germany as 'liberated zones' - i.e. liberated of foreigners and opposition. In the political movements racist action wasn't as blatant, but you saw or heard the comments about change; loss of traditional ways of life; how immigration and asylum seekers were reshaping Europe and America.

Perhaps the rise of the right speaks more of the failure of mainstream politics than the long-term electability of xenophobic protest parties.

The people I met during this time will probably now dismiss me, regard me as a traitor, or try to shoehorn me into their two-dimensional world view. Hate comes easily. I saw its vicitims travelling in convoy down through Slovenia, Croatia and into Bosnia, in the lines of refugees crawling over the border from Kosovo into Albania, when I met families whose sons and daughters had had their throats cut by Islamic fundamentalists (and government death squads) in Algeria. Yet the people I met in the realms of ultra-nationalism would say that they "loved" their race, while it was I who truly hated it.

There would be personal costs of my work, of course: the immense strain on my relationships, the threats... No-one could spend this much time around hatred without consequences. The book and journey seemed to gain a life and momentum of its own. It became an obsession.

I disappeared for months. Few people knew anything of what I was really seeing. Even if I had told them, I doubt they'd have listened. This was separate from their lives - or so they thought. By the end of my journey, BNP leader Nick Griffin was thanking the tabloids for doing his job for him. We seemed to be drowning in a tide of hysteria and isolationism. I had seen how safe lives in leafy suburbs were built on something darker.

Fifteen months after my first encounter with Charlie, the Combat 18 leader would be sitting in the dock, facing a murder charge. I had narrowly missed being caught in bloody civil war as a new leader - a man nicknamed 'The Beast' - took over the gang and attempted to start an international bombing campaign, with the help of Scandinavian neo-Nazis. By the end of it all Charlie was a pathetic figure, a man who destroyed himself and those around him. Even the haters can't live around hatred without suffering the consequences.

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