I'm sitting in a Chelsea café having coffee with the first horseman of the apocalypse. He's very pleasant for a harbinger of doom and is not, as the Bible predicts, holding a bow and arrow but a Granny Smith's apple.

The horseman, or as he is known to friends, Gordon Ritchie, 50, latter day prophet and head of the Jehovah's Witness splinter group The Lords' Witnesses, is quite sure that the Bible refers to him in Revelation 6 when it predicts that the end of the world will be ushered in by four horsemen representing Pestilence, War, Famine, and Death. Naturally, such a claim is bound to call forth the Paxman in any journalist and I decide to put it to the test.

“Do you ride?” I ask.

“Well, I've been pony trekking,” he replies.

To be fair to Gordon, he doesn't go shouting about being the first horseman. It pops up only when we're discussing the Book of Revelation, the last chapter of the Bible so beloved of apocalyptic prophets. The second horseman of Revelation, says Gordon, is War and he is already up and running in the form of George W. Bush. The third horseman, Famine, is loose, too - in the body of the UN which is wrecking the world through its oil-for-food programme, and the fourth horsemen, Death, is in full tack and waiting at the stable door in the form of nuclear weapons.

So who is the first, I ask. Mike Schwingenschloegl, a Lords' Witness who has come along too, gestures towards Gordon. Gordon mumbles a bit and says “That'd be me,” in the manner of a well-bred English gent reluctantly admitting that, yes, he did win an Olympic medal for something but can't remember for what and he'd rather not talk about it.

Gordon is the inheritor of a long tradition of apocalyptic prophecy. The first recorded instances of such predictions are on an Assyrian tablet from around 2800BC which says: “Our earth is degenerate in these latter days. There are signs the world is speedily coming to an end. Bribery and corruption are common.”

It seems for as long as people have been in the world they have been predicting the end of it. The first record of a Christian doomsday cult hails from 156 AD, when the ink was hardly dry on the New Testament. These were the Montanists, who believed that Jesus would return within their lifetime. In the 4th century St Martin of Tours was saying that the Antichrist had already been born and was among us, and theologians down the centuries have been equally as sure and equally as wrong.

I had always thought that there were two forces driving predictions of the Second Coming. The first is an understandable wish for unpleasantness to end, the feeling “the planet's a mess, surely this can't go on”. It's comforting to believe that the vileness of the world is for a reason and that it's going to stop. The second explanation, rather more prosaic, is that apocalyptic conclusions are reached by thick people venturing into abstract thought.

The thing that surprises me about Gordon, though, is that he's not stupid nor, as far as I can tell, mad. I always group apocalyptic Christians in the same bracket as people who think WWE wrestling is a real sport and that The X-Files is a documentary. Gordon, however, looks like a geography teacher and was doing a PhD in aerodynamics until God came calling and has run several successful companies. He was the biggest junk fax distributor in the UK until the practice was outlawed. This makes me see him in a different light.

“Are you sure you're not actually the Antichrist?” I ask him. That is, after all, one interpretation of the identity of the first horseman, and junk faxing is the sort of thing one might expect from the Man of Sin. He just laughs, somewhat maniacally, it has to be said, though not mad maniacal.

Gordon gets his revelations from mathematical analysis of the Bible, in particular the biblical description of time, the details of which are rather esoteric. His predictions have not been rash. They've all been thought through very carefully, but many have been wrong. His revelation came to him after a long period of bible study, including six years in the Jehovah's Witnesses. It all fell into place for him in McDonald's , he says. “I felt like leaping up on the tables, shouting, ‘Why are you eating those burgers?'”

It is his considered opinion that the world ended on March 21, 2008. Are you seeing the flaw in this yet? To be fair to him, he thinks March 21 was just the beginning of the end, Christ warming up for the Second Coming, so to speak, but he has a long track record of incorrectly prophesying all sorts of calamity.

“Admittedly, we have got it wrong before,” says Gordon. How many times? “Over 70 but just because we've been wrong in the past doesn't mean we will be wrong in the future. We've been right about some things. About one in ten of our prophecies are correct.” I wouldn't like to venture into Ladbrokes with that kind of success rate.

Can he give me an example of successful prophecy? Well, take the price of wheat. Gordon predicted the escalation in price and thinks that, within a year, it will be $32 a bushel. Couldn't you have predicted that through studying the Financial Times, rather than the Bible? “Maybe, but would you have had the courage to act on your deduction?”

Faith brings a dividend and Gordon backs his convictions with cash - his main source of income comes from online share dealing, which he does at night, from home in Totteridge, North London. He won't say how much he has earned, but he has obviously made enough to avoid having to get a conventional office job. Hmm, that's my kind of religion. I'm beginning to see why his disciples might forgive him a few bad calls.

The financial success of Gordon's speculations must be some compensation for the depth of humiliation he has had to suffer. “Well, when I went on New York radio in front of two million people telling them they were going to be imminently destroyed and then they weren't, yes, I did feel a complete berk,” he says. Similarly, he took out £30,000 worth of advertising in The Sunday Times predicting that the UN would take overall political control of the world. He ran ads in March, July, September and November 2001, revising his prophecy each time. “Yeah, that turned out to be wrong, duh!” says Gordon.

So what keeps him going? “I know I'm right,” he says. I point out that he's not right, in fact he's very publicly wrong. “Well there's a limit to how many mistakes I can make, I suppose,” he says. “We might get the fine detail wrong but the thrust of what we are doing is correct.”

It is tempting to think that anyone who has these views must be in some way psychologically unhinged. You could look into Gordon's past and see evidence of someone who was unsettled - courses started and not finished, a PhD completed but not handed in, a conviction for mortgage fraud for lying on the forms - but there's nothing that suggests madness. He came from a stable family to whom he remains close; his father was a surgeon in Edinburgh, and a Presbyterian, his mother Church of England. The one thing that stands out in his life, the real turning point, is when the Jehovah's Witnesses knocked on his door back in 1989. Religion seemed to give him the direction he had lacked up until that point, though he was later “disfellowshipped” when he came up with his proof of the end of the world and refused to back down, he says, and that's when he set up his own group. So what are his latest predictions? We meet in late April. He says there will be a terrorist attack on the weekend of April 26 in Europe and the US. Er, no there wasn't. On May 12, angels will start appearing to people, just popping up at dinner parties or when you're watching TV. I feel sure I would have noticed that. Don't book your holidays for next August because, by July half of mankind will be toast and we'll be ready for the new kingdom of Christ, he says.

Gordon is a self-effacing, modest prophet who seems like a very nice man. That said, he has managed to convince himself of the truth of an approach to Bible study that, at best, has a history of utter failure, and at worst - my interpretation - is a complete load of rubbish. I'm not the only one to take this view. Gordon's girlfriend of 16 years finds his faith exasperating. “She just wishes I'd forget all about it and we could get on with living a normal life,” he says.

But does he even hope his predictions come true? Gordon says he's looking forward to the Second Coming but I can't believe he's welcoming the extermination of 50 per cent of mankind. “They won't actually die,” he says. “Their spirits will inhabit angels until they decide to join the Kingdom of Heaven. If Mike here were to get hit by a bus his body would just enter another vehicle.”

Yes, I suppose it would. But what about his friends who don't believe? He does have those, including his brothers.

“I do worry about my brothers sometimes but there are a lot of things supposed to happen before the end, albeit in rather a small time, so they should have plenty of opportunity to wake up,” he says. And even if their bodies are killed, their souls will live on and have a chance to repent.

When Christ returns as ruler, says Gordon, he will purify mankind and put in 144,000 kings ruling in kindly dominion over the earth. By lucky chance both Gordon and Mike will be kings. They're both very pleasant and I suppose they can't do any worse than the present lot of rulers.

He must feel, though, that the whole world is living in a dream and that he just wants to shake people by the lapel and alert them to the truth.

“Yeah, that's what I'm doing,” he says.

What if he is wrong? I suspect he will be OK. His attitude seems to be that he thinks the Apocalypse will happen in his lifetime, but if it doesn't, it's not the end of the world.

They thought it was all over

March 25, 970: Logicians foresaw the End when Annunciation and Good Friday fell on the same day, believing that it was the day that Adam was created, Isaac was sacrificed, the Red Sea was parted, Jesus was conceived, and Jesus was crucified. February 1, 1524: London astrologers believed a flood would destroy the world; 20,000 people abandoned their homes.

October 1, 1914: The author and minister Charles T. Russell created the most hyped Armageddon date for Jehovah's Witnesses after an 1881 prediction didn't materialise, picking out quotations from the Book of Daniel and assigning them random numerical values to come up with this date.

Friday, February 13, 1925: Young Margaret Rowan predicted the End after having a dream of Angel Gabriel. A man then spent his life savings on advertising space for an eleventh-hour gathering. When nothing happened, he suggested that perhaps she meant Pacific time.

2006: A British cult filled caves in India with dry goods, believing the end was nigh.

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