Here I am, one bright but blustery Tuesday morning, inside the wrought-iron Victorian shell of London's Marylebone station, surrounded by Beatles fans; mostly Americans, with two Canadians, three young Aussies and a sprinkling of continentals.

In their midst stands Richard Porter, spry but diminutive. If you can warble a "yeah, yeah, yeah" while shaking your mop top, then listen up. For the modest sum of £6.50, Richard will share with you his Beatles facts and obsessions. He declares that here, on this spot, on this very concourse, the opening scenes of A Hard Day's Night were shot in March 1964. As the lads ran along the station platform, chased by a horde of screaming girls, George Harrison stumbled. "He actually hurt himself," says Richard. "It was an accident - but they kept it in the film. Some of those chasing fans received signed photos, now worth a packet."

Gert, from Dortmund, raids his knapsack, as if about to produce his very own copy, but all he's got is a packet of sandwiches. Gwen from Miami - who's on the verge of 64 - looks disappointed.

We are at the start of Richard's In My Life walk, a way-above-average Beatles trail through London. He talks in a blizzard of rapid info-bites, torrents of facts scything through traffic noise as he leads us past the beautiful station entrance, crossing the road towards the pillared facade of the Marylebone Registry Office and Magistrate's Court.

John and Yoko made an appearance here, on a drugs charge, in 1968 - a fact which, amid all the swirl of info, Richard omits. Instead he tells us that "Paul married Linda here in 1969 - on March 12. People said it wouldn't last. But how wrong they were." We pause to reflect on Linda's sad absence. "The fans had gathered here that day to cry their eyes out," Richard adds. Paul was the last unwed Beatle. "And such a commotion was raised that Paul slipped in unnoticed through the back." Richard extracts a black-and-white photo from his bag to prove the point. It's Paul looking cheery among the bins.

George didn't make it to the wedding. That afternoon at his house in Surrey, a sniffer-dog, Yogi, turned up a cache of marijuana. George wasn't amused. And then it turned out that he hadn't been invited in any case.

Richard, imparting these sacred tidings, is losing his voice. He gamely yells that Ringo Starr and Barbara Bach were also married here in 1981. "They met on a film called The Caveman - not the best film of all time." On this occasion Paul and George turned up with their wives - "the first time the Beatles had been together in many years". John Lennon, alas, had been assassinated in New York months before.

On a brighter note for all couture buffs, Richard appends the salient detail that Barbara's dress was run up by those spangle gods "the Emmanuels, who'd designed the fairytale wedding frock of Diana, Princess of Wales". Two young Bostonians standing beside me are visibly thrilled. Steve, the blond, utters an "ooooh" and clutches the hand of his partner, Brett. "Gee, I love it Brettzo, don't you just?"

Richard is grooving now, leading us off towards Ringo's old love pad, a Regency flat off Gloucester Road. There, at 34 Montague Square, John and Yoko once posed nude for their brown paper bag pics, exhorting the world to give peace a chance.

But today, the people who live inside aren't getting much privacy, or peace. Richard permits us a moment for photos, then mentions that Jimi Hendrix (cue more ooohing) had once holed up at this quiet address.

A skiff of rain begins. We leave. Ten minutes later, down on Wimpole Street, we hog the narrow pavement outside the former home of Dr Richard Asher. Dr who? It transpires that Asher's daughter Jane (the one now famous for acting and cakes, but mostly for cakes) lived here with her parents - and her boyfriend, Paul McCartney. "Here, in 1963," Richard says, "Paul awoke with a catchy tune in his head." He had dreamt it. As Paul duly strummed the tuneful chords, he added some lyrics. Richard pauses, then recites Paul's rhyming couplet: "Scrambled eggs, baby, baby how I love your legs." The lyric didn't quite have the wistful effect that Paul was after. So, he rewrote it, calling it "yes, you guessed it, Yesterday. The most famous Paul McCartney song of all time." Richard reels off the millions of times the song has been played on American wirelesses, the tally of cover versions, blah, blah.

His daunting appetite for Beatlefacts is inspiring, as is his energy. We scurry.

Outside the grey, deserted, derelict facade of EMI House in Manchester Square, Richard defies the drab surroundings: "Here, the Beatles played their balcony scene for the cover of Please Please Me - their debut album, released in May 1963. EMI have moved to Hammersmith and have taken the balcony with them." Taken it with them? Thankfully, Richard draws the line at pursuing the balcony. He opts instead for the Jubilee line to that mecca, Abbey Road. "American fans have actually got on their knees and kissed it," Richard says, pointing vaguely at the iconic zebra crossing that the Fabs bestrode on the cover of their Abbey Road LP. We stop the traffic, aping our heroes.

The walls in front of the famous studios are smeared with a million cliches, longstanding graffiti proclaiming the fans' undying love and mystical thoughts. Here, 15 years ago, Paul McCartney appeared while Richard was doing his tour. Springing chirpily from his limo, Paul consorted with the fans before vamoosing to cut his album. Richard had captured the moment. Snap!

We are agog.

For there it is: Paul looking cherubic. As does Richard, standing before us now, irrepressible, and so likeable that you wish you could set him to music. Will lightning strike twice? Will a Beatle casually materialise? Will Steve burst? Brett flashes a look that warns: "Let it be!" But Richard is talking again, more facts, more memorabilia.

Yeah, yeah, yeah.

Need to know

  • The London Walks brochure is available by calling 020 7624 3978. Details at .

The Beatles In My Life walk operates from Marylebone Station on Tuesdays and Saturdays at 11.20am.

  • easyJet flies daily to Luton and Stansted from Glasgow and Edinburgh, and to Gatwick from Edinburgh. or 0905 821 0905.