In the footsteps of a Time Lord

Trails of the unexpected: for Doctor Who fans, London is full of sacred sites, from Cybermen in St Paul's to Daleks trundling in Trafalgar Square.

You find me making my way down Ladbroke Grove one wet morning. Not a good place to be at the best of times, and today the weather is being particularly spiteful. But then I see what I'm after - the John Nodes funeral parlour. Lovely. I check with my rain-sodden sketch, get my camera out and take a picture. Happy now, I consult my A-Z under a shop doorway - only half a mile to Willesden Lane Cemetery. I pull my hood tighter, jam my bundle of sketches into my anorak pocket, and set off once more down the dreary road to Kilburn.

All right, I made the anorak bit up, but in every other way I am a Sad Fan. More specifically, a sad Doctor Who fan. How can I call myself anything else when I spend my spare time hunting out locations used by the programme umpteen years ago? Not for me the lure of Perugia or Peru - I feel happier on a street corner in Perivale. (It's where they filmed the last ever BBC Doctor Who story - in case you didn't know.)

London has by far the highest concentration of Doctor Who-related sites because the BBC is based in London, and it makes economic sense to film on its doorstep. So let me take you back through the mists of telly nostalgia.

Let's begin at Trafalgar Square. In 1964, long before the riots of 1990 and a week ago, this was witness to another kind of invasion altogether, as the Daleks displayed their mastery of the planet in the aptly titled The Dalek Invasion of Earth. Shots of Daleks gliding around the supposedly deserted square were taken one early morning in September, although a double-decker bus can be seen in the background. In 1973, the same trick was repeated to show a London evacuated following the Invasion of the Dinosaurs.

Just a minute's walk away is Covent Garden. It was here, in 1966, that the Army took on the might of the War Machines, box-like tanks created by super-computer Wotan, housed in the then Post Office Tower. Amid the fruit and veg stalls, troops fought a pitched battle with the (single) War Machine, dodging explosions and flying groceries. Nowadays, it's all twee gift shops and performance artists.

As an aside, the production team were hoping to film the bed-wettingly scary 1968 Yeti story The Web of Fear in Covent Garden and Aldwych Underground stations. But London Transport wanted pounds 200 an hour to film there (and then only between 2am and 5am), so the BBC mocked it all up at Ealing film studios. So good were the sets - or so grainy was the monochrome picture - that London Transport complained that they had filmed there without permission.

Across the river from the Aldwych, we come to Waterloo East railway station. In April 1988, the streets under the station were taken over by two Dalek factions fighting for supremacy in the Sylvestor McCoy story Remembrance of the Daleks. As the newly introduced Special Weapons Dalek blew its opponents into little pieces, explosions ripped across the streets, alerting local residents to what must have been anIRA bomb. Soon London's emergency services were on the scene, to be greeted by a fleet of Daleks appearing from the smoke and debris.

The Thames has featured only twice as a location. Most recently, the Loch Ness Monster reared its ugly head from it in 1975's Terror of the Zygons - a hideously unsuccessful special effect. But in 1964 it provided The Dalek Invasion of Earth (again) with a far more iconic image - a Dalek emerging from icy depths. Filmed below Hammersmith Bridge, where the BBC's Riverside Studios once were, it featured Dalek operator Robert Jewell sitting inside the Dalek casing in a wet suit as the machine was winched out of the river with a rope. The message was clear: nowhere is safe from these metal monsters.

West of Hammersmith we come to quite possibly the premier Doctor Who location - none other than Marks & Spencer on Ealing Broadway. To the uninitiated, it may seem like just another department store, but to those of a certain age, it is the stuff of nightmares. On 24 January 1970, towards the end of Jon Pertwee's first adventure, Spearhead from Space, the nation looked on in horror as ordinary window dummies suddenly jerked into life, smashed their way out, and began massacring innocent bystanders. Thirty years on, it's still recognisably the same place, and I still feel a frisson of excitement as I glance at the current mannequins in their stilted poses.

Close by in Acton is a disused Guinness factory on Western Way. Cybermen, Autons and Martians variously fought the Brigadier and his secret paramilitary organisation Unit here. A Pickfords warehouse along the same road was a (not very secure) prison for a Tyrannosaurus Rex in Invasion of the Dinosaurs. Unfortunately, the televised scenes of a Muppet-like model shouting "Roar!" was more reminiscent of The Goodies than Jurassic Park.

Even further out is the suburb of Perivale, from which the seventh Doctor's sidekick, Ace, hailed. Filming (or, to be pedantic, videoing) took place there in June 1989 for Survival, an ironic title, for it was the last BBC story ever transmitted. I paid homage there not so long ago, and stood outside the house on Colwyn Avenue where the Tardis made its final resting place. Then I toured Ealing Central Sports Ground, where giant horse-riding cats threatened Ace, and later went to Londis Food Market where comedians Hale and Pace played grocers.

While Perivale is unchanged, some locations bear little resemblance to their TV counterparts. The 1988 Cybermen story Silver Nemesis was filmed in a huge derelict hanger on Greenwich Peninsula. Soon after completion, the building was razed. Now another empty hanger sits there - the Millennium Dome. And in 1984, the production team took over abandoned warehouses in Shad Thames, just east of Tower Bridge, to stage the Resurrection of the Daleks. Machine-gun-wielding policeman and exploding Daleks brought the derelict site to life, but only a year or two later the area had fallen into the hands of yuppies, and one of the most atmospheric film locations in London was no more.

Let's end the tour almost where we started - on Blackfriars Embankment, and the terrifying scenes of Cybermen emerging from the sewers in the 1966 adventure, The Invasion. The old man-holes are long gone, but you can console yourself with the view up Peter's Hill to St Paul's Cathedral, made famous by that chilling image of Cybermen marching down the steps.

Time's up and I never mentioned Fitzroy Square, BBC TV Centre or British Oxygen's HQ, all prime Doctor Who locations. Perhaps another time. Oh, and I didn't lie about the anorak after all - it's green and very cosy, thank you.