There are, as ever at King's Cross Station, significant queues. There's little interest in the actual trains, though. For many arriving at the London rail hub, this is a literary pilgrimage rather than anything as simple as a transport interchange.
To any Harry Potter fan, King's Cross is the home of Platform 9¾, where the magical Hogwarts Express departs for Britain's secret wizarding school. And readers were coming to the station to find it not long after the first of J K Rowling's boy wizard books was released 20 years ago.
Originally, station staff were bemused but tolerant of this. Then, later, came the realisation that money could be made out of the whole thing. A platform sign went up – at the side of Platform 9, rather than between platforms 9 and 10 – and a sculpture of a luggage trolley disappearing through the wall was installed. Now, people wait patiently to have their photos taken there, with staff on hand to furnish props such as wands and scarves in Hogwarts house colours.
There's plenty more of that sort of thing for sale in the neighbouring Harry Potter Shop, which does a roaring trade in Hedwig the owl key rings, Marauders' Map T-shirts and Dobby the elf dolls. It's fair to say that the Rowling fantasy world has become a lucrative business.
But King's Cross Station is not the only place in London with a Harry Potter link – and the Tour for Muggles strings a few of the others together.
When meeting outside London Bridge, it quickly becomes clear that there will be few concessions to the Potter-ambivalent. Guide Steph Black (not her real name, but she is gleefully playing up to being a member of the "illustrious" Black family from the books) quickly gets everyone to put their hands into the middle of a circle and swear an oath.
"It's going to be that sort of tour," she says unapologetically. "You may as well commit to it."
The first stop is Borough Market, which ordinarily is an undiluted heaven for the peckish. The target here is El Pastor, a taco-and-burrito joint that was a florist at the time of filming the third Potter movie. Then, it doubled as the entrance to the Leaky Cauldron and gateway to Diagon Alley.
Black digs out film stills from her backpack, showing the street scene dolled up for shooting, with the Knight Bus heading down the road. That, it turns out, was an ordinary London double-decker that had the top shaved off and a movable extra deck added. This extra deck had to be removed pretty much every time the production crew wanted to get it under a bridge.
It is this sort of detail that makes the tour more than just a traipse round locations that were in the films at some point.
Sure, it's quite cool to see the Millennium Bridge that the Death Eaters destroyed, or the government building that Ron Weasley was sneaking around as the gang tried to break into the Ministry of Magic – but the tour is primarily about enriching the fictional world, rather than pointing out its real life stand-ins.
Black tells stories of how the child actors were asked to write an essay on their characters by director Alfonso Cuarón – Emma Watson wrote 16 pages, but Rupert Grint did nothing, then bluffed it by saying it is what Ron would have done. She explains how Rowling's studies of the classics made its way into character names – Remus Lupin's first name came from the wolf-reared founder of Rome, for example. And she kills time on Tube journeys by asking questions with multi-choice answers, then dividing people into Hogwarts houses based on their answers.
For someone who read the books as an adult, saw a couple of the movies and generally quite likes the whole Potter thing, without being a massive fan, the enthusiasm and level of knowledge becomes infectious. Especially when surrounded by awestricken children continually asking questions of a guide who has to properly know her stuff to survive the barrage. It's a reminder that Rowling created an impressively detailed, complex world. And given that most of the children present wouldn't have been born when the last book originally came out, it seems Rowling has not just got one generation into reading, but the next one, too.
As for the locations, the most fascinating ones end up being not those used in the films, but those that Rowling had in mind when writing the books. The final stop, for example, is Cecil Court. It's a wonderful little lane that pays scant regard to outside modernity, full of specialist bookshops, antique dealers and picture framers. It's very clearly the inspiration for Diagon Alley, and when you see it, you start to grasp how blurred the boundaries between the magical and muggle worlds are.
Nearby in Theatreland you can witness the latest incarnation of the Potter machine – Harry Potter and the Cursed Child at the Palace Theatre. The play, which focuses on Harry's son going to Hogwarts, has been running since July last year, while tickets for the Broadway version in New York will go on sale next month.
But despite Potter being such a juggernaut, it is still possible to uncover a few little edifying secrets. Just behind the theatre is the House of MinaLima, the shop/gallery showcase for graphic artists Miraphora Mina and Eduardo Lima. The pair met on the set of the Potter films, and did a lot of the graphic art for them – much of which is now on display in the squeezy exhibition rooms upstairs.
Scattered around are books about Mudbloods, Ministry of Magic identity cards and Weasley & Weasley joke shop dung bombs. Nothing individually is all that remarkable, but these props are the little ingredients required to bring the books to life on film. Twenty years on, spells are still being cast.
Potter more? Other UK Harry Potter locations
Warner Brothers Studios, Leavesden: The Making of Harry Potter tour goes into the props, monsters, costumes and special effects for the movies in the place where the bulk of them were shot. Advance booking is required, via wbstudiotour.co.uk
Christ Church College, Oxford: The college's Hall doubled up as the Great Hall in Hogwarts, and is open for tours. See chch.ox.ac.uk
Alnwick Castle, Northumberland: Often used for sequences shot in the grounds of Hogwarts – including numerous flying broomstick moments – Alnwick Castle also offers 'broomstick training' sessions. See alnwickcastle.com
Glenfinnan viaduct, Scotland: When the Hogwarts Express makes its way to the school in four of the Potter films, it crosses over this outrageously pretty viaduct on the West Highland line. Quidditch matches, meanwhile, were filmed in front of Glen Nevis near Glencoe.
Visit Britain has a list of Harry Potter locations on its website
Potter online
For those unable to travel, fans of the books and films can now fly through the boy wizard’s Hogwarts School and quidditch pitch in an immersive digital experience.
The Hogwarts Experience was launched on fan website Pottermore to coincide with the September date when 11-year-old orphan Potter started at Hogwarts school in Harry Potter and the Philosopher's Stone (1997).
This free digital experience allows fans to fly through the exterior of the castle and the quidditch pitch.
Abu Dhabi live concert
Later this month Harry Potter and the Philosopher's Stone will be shown on the big screen at Abu Dhabi's du Forum, and it will be backed by a live orchestra. The fun will take place from September 21 to 23. Go to www.harrypotterinconcert.com for more.
