I am sitting in the upstairs coffee shop at the Virgin megastore at the Tottenham Court Road end of Oxford Street in London. Opposite me is Andy, mid-thirties and glasses (like me), but (important difference) hair down to his shoulders. He looks like an engaging relic of the Seventies. Andy works for a travel organisation and lives in Croydon, south London. Outside work he plays bass in a band and runs a stall at record fairs. What brings us together is our mutual passion for Led Zeppelin.

I am a collector, too, but not on his scale. I have a few 'nice items': the rare Zep single costing pounds 180 that my wife and family bought for my birthday and which I had been mooning over in a second-hand record shop for weeks (the people at the shop had a great laugh by telling me it had been sold); a couple of German club editions worth pounds 100 each; a live Yardbirds album that Jimmy Page injuncted when the record company tried to cash in on Zep's success (say pounds 30); and mint copies of all the official releases.

Andy, though, is on a different plane. He has been collecting since 1974. He knows Dave (manager of a second-hand record shop), another UK authority on all Zep matters. They know Howard (lives in Brighton), who wrote the first biography of the band (I have it) and of Jimmy Page (ditto), and has a third book out. These guys are almost as famous to the cognoscenti (ie, plebs like me) as the band itself. And I am about to be allowed to enter the magic circle, for, over the previous few weeks, I have handed over several hundred pounds to Andy and am here to take delivery of what will be the centrepiece of my collection.

People like us are on the edge of acceptable rock fandom, but we are beyond redemption, having descended to the penumbra of fanzines (home-produced newsletters devoted to particular bands). Andy edits one on Zeppelin. So does Dave. And this was a band that folded 14 years ago (two years more than it was in existence) when its drummer, John Bonham, died at Page's house.

We may be risible brain-deads, but we still read Record Collector every month. RC looks as if it were last redesigned in the Fifties, but for the serious music fan it is the only publication worth getting. Here are all the useless ephemera of label colours and pressing dates, which would stand you in good stead on Mastermind. And at the back - joy of joys - are pages and pages of advertisements from collectors offering items for sale. It was here that I found my Jimmy Page lunchbox (video and CD of his Outrider album) now going for as much as pounds 100 (imagine my excitement as I collected the package from the PO); here, too, I spotted the phone number of Gary in Southend who sold me a Spanish pressing of 'Muchisimo Amor' ('Whole Lotta Love') coupled with the expressive 'Ruptura Communicaciones' ('Communication Breakdown'), here that I - well, I could go on.

But if you think I am mad, consider Rick, another of Andy's circle. He buys different Led Zep pressings. The record may be the same, but Rick can tell you in which factory it was made. He collects as many copies as there were factories pressing it. He has 60 copies of some releases.

Like all disciplines, record collecting has its own language. Investment grade goes from Mint, through EX (excellent), down to VG. Good is just about acceptable. Fair, Poor and Bad are junk. All records have a double grading, the first for the cover, the second for the disc. So collectors tend to speak in a kind of cross-eyed double-Dutch, using terms such as Mint/Mint or EX/EX.

Your average collector knows to the nearest 10 quid what is well priced or not. (I once saw a Zep rarity quoted in the back pages of RC at just over half its actual value. I rang. It had gone. Yet that issue of RC had been out only a few hours.) But collectors also have a strong sentimental streak: you know when you are being ripped off, but you do not care because you want the item.

There is another minefield, that of the 'boot' (for bootleg) recording: unauthorised, usually of the band in performance but sometimes rehearsal tapes or studio out-takes. It is not illegal to buy these, but it is illegal to trade in them. RC will not run advertisements for them. Less suspect are 'promos' (promotional recordings), copies sent to radio stations or review copies to magazines, although technically these remain the property of the record company.

Zep's manager, Peter Grant, waged war against bootleggers during the band's lifetime, not least because this black-market trade is a significant leech. Nowadays, Jimmy Page and others recognise the value of these recordings, which represent a colossal historic archive. In Zep's case there are more than 500, one of virtually every concert they played. Some are poor quality - recordings made by a bloke in the crowd with a mike on a broomstick. But some are recordings directly from the mixing desk where the band's onstage sound was actually controlled, and are of sufficient quality (virtually studio perfect) to be issued on CD.

The studio out-takes (alternative or primitive versions of songs, not officially released) are from highly dubious sources, as are tapes of work-in-progress, the theft of which has been the bane of Page's recording career. Who buys these things? After all, even an act such as Zep, at its best live (I know, I was at Earls Court in May 1975, arguably its finest hour - or three hours), played the same stuff night after night. Well, believe it or not, there is a Canadian who has listened to every single bootleg recording ever made, and noted the quality of each including the running order of the songs performed and any variations ('Jimmy sounded a bit out of it the following night at Stockholm'; 'This time they reverted to the 'Out On The Tiles' intro to 'Black Dog' '). This feat of scholarship took him 10 years.

Crazier still are those collectors specialising in first editions of bootlegs - inspired by the fact that, since boots by definition lay themselves open to pirating, many are third or fourth generation copies.

Andy agrees that the collecting thing has gone a bit too far. Each copy of his magazine is now numbered in response to collector demand. He is often asked for a low number, which he is requested to sign (yes, him, Andy]). As he says, 'People are buying the store displays.' That is, posters and cardboard cut-outs issued to shops to promote a release. These, along with such things as concert programmes and backstage passes, are known to collectors as 'paper goods'.

'It's getting so that it isn't enough to have the music. You have to get these other things to stay close.' For example, the Zeppelin blimp, a 3ft inflatable Zep balloon issued to stores as a display at the time of the Remasters release, now fetches pounds 120.

Above all, Andy has met The Man, Jimmy Page himself, twice. Once at Robert Plant's bash in the Old Rangoon after the Hammersmith gig ('We chatted for over an hour, and Jimmy was charming'), and once before the Firm's gig at the NEC (I went to that and to the earlier one at Wembley, but Andy went to them all), in the bar where Page was knocking back pints of lager with wine chasers to calm his legendary nerves.

Andy's mate Simon actually knocked on Page's door when the maestro lived in Windsor, on three different occasions. Twice he did so in vain: the first time Page was out, the second time he was in but pretended to be out. But the third time he was successful: Jimmy invited him in and granted him an audience of more than two hours.

My only half-anecdote concerns Bill Wyman, whom I saw at Geneva airport in the mid-Eighties. He sat opposite me on the bus going out to the plane and I asked the only question that really interested me: 'How's Jimmy Page?'

My hero, rocked by the death of his drummer and the break-up of his band, had fallen from sight and had been in court on a stupid charge of possession of drugs. I knew they knew each other: the Stones had let Zep overrun when recording Presence, even though they had the studio booked; and Keith Richards and Page were known to exchange notes on alternate fingerings of licks (runs of notes) and riffs (runs of notes and chords, repeated to form the basis of a song). Wyman reassured me about Page: 'He's better. He's cut his hair.'

After an hour and a half of chit-chat, Andy has to go. He is organising the next Zeppelin convention with Dave, and they are hosting a meeting of 40-odd people to discuss the details. He hands over the worn- out yellow carrier bag, propped negligently by a table leg, the thing that I have paid all this dosh for. What is inside is almost as tatty: a battered copy of Led Zep II, an album I already have, both in its vinyl original - M/M, plum/orange label - and on CD. The difference is that this one bears four scrawls in blue ballpoint, one of which, Pagey's, I recognise. (I was the crazy kid who, years ago, went to Companies House and got them to bring the file of James Page Music Limited out of the basement just so I could marvel at his signature on the forms). An accompanying scrap of paper signed by Alan, part of the network, tells me where the signatures of all four band members were obtained (Colston Hall, Bristol, when they performed there in 1970).

Since Bonham is dead, I would not be able to get this now. Is it a fake? Possibly. If not, will it increase in value? Probably, but not for at least 10 years. But that is not why I want it. This, for me, is to be treasured for life. I doubt if I will ever sell it.

Now, weeks after I collected the album from Andy, I turn that tatty bit of cardboard over in my hands and am suffused by a warm glow. I know for sure it is genuine. How? Easy. Alan's note says the band signed it on 8 January 1970; they did perform there that night - I have checked. I collected it from Andy on 8 January 1994. Pagey's 50th birthday was on the ninth. That is how I know: it was written in the stars. What greater proof do you want? The Three Wise Men set out on less.

John Windsor's collecting column returns next week.

(Photograph omitted)