"When people see red street furniture they tend to think of London," says Helen, our tour guide, as we hit the streets of Cardiff. "So when the Doctor Who producers need to turn this city into London they simply splash a lot of red about and viewers' imaginations do the rest."
She pauses for a moment. "But have a close look at the scenes pretending to be filmed in Oxford Street … and you'll clearly see that at the end." That, as pointed out by her outstretched arm, is Cardiff Castle. Who knew?
Certainly not me. And I'll admit that as someone who has had an on-off relationship with Britain's favourite Time Lord – everything between Tom Baker and David Tennant is a black hole to me – I was a bit anxious about joining a clutch of fervent Whovians, as fans are known, on a three-day Doctor Who tour.
Helen, a young woman refreshingly blithe about her ownership of "a Dalek hot water bottle with a button on it that makes sounds" and who handed out her own home-baked Tardis-topped cup cakes, put my mind at rest. "We'll be watching relevant episodes and clips on the mini-coach before we arrive at each location, so you'll know what to look out for."
The tour begins in London, and there was barely a street to which she couldn't attach a scene or two. A visit to the Doctor Who Experience duly got me up to speed with the Doctor's many adversaries – I particularly cherished a 3D encounter with a Weeping Angel. They're OK, as long as you don't blink – "Blink and you're dead," the Doctor famously warned.
The next day, and two full episodes later, we are in Gloucestershire's Forest of Dean. The unsettling rock formations of Puzzlewood were created by iron ore mining going back to Roman times.
"Steven Moffat changed the script of the Flesh and Stone episode just so that they could use it," Helen tells us, handing out stills so we can track down the exact stone on which Amy Pond (the Doctor's current companion – do keep up) almost breathed her last. Up the road at Clearwell Caves shock and awe await us: the scary paintings daubed on the walls for The Satan Pit are still (just about) visible and, what is more, can be touched.
That evening, at the Wyndham Arms Hotel in Clearwell village, we are plunged headlong into a Doctor Who pub quiz. Sadly, even the successful trawling of my childhood memories for the number plate of Jon Pertwee's car (it's WHO 1, if you're taking notes) is not enough to drag me up from an ignominious last place.
But I refuse to be downcast. The programme's location spotters clearly know a cracking backdrop when they see one and the views we are treated to the next day are astonishing, with the Brecon Beacons looking particularly striking in the sunshine.
In Cardiff, we install ourselves at the Maldron, a hotel that sounds suspiciously like a Dr Who villain. The Welsh capital is home to the programme's studios and provides a copious array of locations, around which Helen shepherds us with an infectious enthusiasm. So infectious, indeed, that when I look out from my ninth-floor bedroom window that night on to Cardiff Central station, I couldn't help but recognise it as another Who hotspot.
By journey's end we have recreated a number of famous scenes and visited a dizzying array of locations, including two castles, two churches, a Victorian gothic mansion complete with secret passage, a beach, a cathedral, Stone Henge, the charming villages of Llandaff and Skenfrith (aka Leadworth – "an anagram of Dr Who Tale", and Amy Pond's home – and Upper Leadworth), the Welsh Assembly building, an American diner and a stand-in for Versailles.
It seemed impossible to achieve all this in just three days. Unless, of course, our mini-coach was itself a Tardis. Thinking about it, it did feel quite roomy inside …
• Brit Movie Tours' next Doctor Who Tours (0844 247 1007, britmovietours.com) begin on 19 August, and 1 April and 27 June 2012; adults £480, under 12s £440, including two nights' B&B accommodation, transport and entrance fees. Four-hour Doctor Who tours of Cardiff cost £21 for adults and £19 for under 12s; three-hour London tours cost £25/£20
