"So where do you keep your Dalek?" Colin Young, 39, hospital cook and Dr Who afficionado, nods in the direction of the hall. "In the spare room," he says, "with the Zygon."

The first thing we see is a full-sized Dr Who pinball machine and a cabinet of assorted disembodied alien heads with slack-jawed expressions, but from behind a forest of artwork and Dr Who advertising material, a sink plunger emerges, pointing menacingly in our direction.

We help move the assorted memorabilia, and there it is: a 5ft-tall murderous extraterrestrial mutant with an endearingly skewy plunger, mounted on wood.

Colin has a Tardis too, which was made for a play on the Fringe in 1983, though for storage purposes it's in bits.

But neither the Tardis nor the Dalek are the star attraction of this extensive collection: that is Colin's servo robot. What's a servo robot, you may ask. "It's THE servo robot - there is only one," responds Colin. As proper Dr Who fans know, the servo robot appeared opposite Patrick Troughton in 1968. It may look like a Blue Peter job, a 4ft hollow shell spray-painted silver, but to a Dr Who fan - or Whovian - it's like part of the Crown jewels.

Colin went to London to collect it and brought it back on the plane. "There were a few funny looks," he says.

Colin bought his first piece of Dr Who kit in 1974 from a shop on Bonnyrigg High Street, a yellow battery-operated Dalek, and has been seriously collecting Dr Who memorabilia since 1980. Shelf upon shelf of books, DVDs and videos fill his bedroom, and there are toys, records, costumes and original props in every corner, not to mention artwork from books, comics and publicity material. He has around 2000 photos, including production photos taken on set: these days, the BBC comes to him, such as when it needed pictures for a DVD extra feature. It's no surprise, then, that Colin is also the moderator on a collectors' website - www.richardwho.com.

But though this is a labour of love, the collectibles are valuable and are specially insured. One of his most revered possessions is a Cyberman mask from the 1968 Patrick Troughton story Invasion. He has been offered £5000 for it, nearly 10 times what he paid. He also sold one of two Dalek games for £1800, when he'd paid £700 for both.

Every Dr Who fan has his favourite and Colin's is William Hartnell who left in 1966. So what does he make of Russell T Davies's version? "Frankly, they're children's programmes," he says. Where the big business of Dr Who collecting is concerned, though, the boom can only help.