When Eddie Redmayne began dating Hannah Bagshawe in 2012, he felt the need to warn her about embarking on a relationship with an international movie star. At the time he had a series of roles lined up that looked, on paper at least, like they’d take him all over the world.

‘I said to her, “You know, with my life there could be a lot of travel, we could be nomads” – but she was all up for that,’ he recalls. ‘I then made Les Misérables, which was set in Paris, The Danish Girl, which was set in Copenhagen, and Fantastic Beasts and Where To Find Them, which was set in New York…’ And? ‘And all of them were shot in Watford.’ Or Ealing. Or Slough, even.

Bagshawe and Redmayne can’t have been too disappointed. The pair married in 2014, the same year the thoroughly Cambridge-set The Theory of Everything, for which Redmayne would win an Academy Award, was released.

In a couple of weeks he will return to the big screen with the follow-up to Fantastic Beasts – the Harry Potter spin-off written by JK Rowling and produced by the same team as the Potter films, in which he starred as Newt Scamander, an eccentric English wizard zoologist who ends up fighting for good against evil with a motley band of acquaintances.

When he read Rowling’s script for that film’s sequel, Fantastic Beasts: The Crimes of Grindelwald, he noticed that much of the action takes place in Paris during the années folles (‘crazy years’) of the 1920s. Bagshawe was thrilled. Redmayne was suspicious. ‘Nope, Watford again.’

Under feeble autumn sunshine, Paris-upon-Watford wasn’t looking too bad last November. At Leavesden studios – Warner Bros’ filming complex in the Hertfordshire hinterland – whole boulevards of the French capital had been constructed in preposterous detail, complete with working shops (themselves complete with tills), fountains and cobblestones.

To a visitor, it was extraordinary, but building new worlds is the purpose of Leavesden.

Over 80 hectares, there are approximately 50,000 square metres of stages, one of the largest heated water tanks in Europe (it takes 10 days to fill), production offices, and a 32-hectare ‘backlot’ with a 180-degree uninterrupted vista – making it ideal for a battlefield, say, or constructing an historic European city from scratch. It was here that all eight of the Harry Potter films were shot.

It’s also here, on the other side of the car park, that thousands of ‘Potterheads’ arrive every day to experience The Making of Harry Potter – a permanent exhibit that allows fans to wallow in nostalgia by wandering around original sets and poking real props.

Rowling’s magical universe is expanding further with The Crimes of Grindelwald. Under the code name ‘Voltaire’ (designed to stop details getting into the wrong hands), the film was on the fifth day in the 19th week of 22 spent filming, and there was an atmosphere of ‘we’re nearly there’ about the cast and crew.

Hundreds of people swarmed the site, having worked for much of the year constructing sets, designing props, preparing characters and working with the latest technology to figure out just how to put Rowling’s ideas on screen.

‘Every time Jo delivers a new script it feels like we are diving into a new experience, rather than returning to an old one. She’s constantly reinventing and expanding the world she has created,’ says David Yates, who directed the last four Potter films and remains at the helm of the Fantastic Beasts series. ‘The first Beasts had a lot of whimsy and charm, the second has layers of mystery and intrigue. [It’s] more of an emotional thriller than a fantasy adventure.’

In 2016’s Fantastic Beasts and Where To Find Them, a box-office success inspired by Rowling’s 2001 book of the same name, Newt was a bumbling academic with a briefcase full of magical creatures – everything from the Niffler, a mischievous platypus/mole thing with a magpie’s eye for anything shiny; to the Nundu, a ferocious, giant leopard with disease-laden breath that can move in silence.

He met an unsuspecting non-magical man, Jacob Kowalski (played by Dan Fogler), in New York, and the beasts were let loose. They also met two magical sisters, Tina and Queenie (Katherine Waterston and Alison Sudol), as well as Credence Barebone (Ezra Miller) – a young man initially believed to be non-magical, but who was in fact a powerful Obscurial, a wizard or witch who develops a dark parasitical force as a result of their magic being suppressed through abuse.

Keeping up? Good. Flitting around New York rounding up beasts, Newt, Jacob, Tina and Queenie soon encountered the unsavoury forces of the wizarding world in the 1920s, while Credence found out more about his powers. The film ended with its villain, Percival Graves, a kind of corrupt politician played by Colin Farrell, being revealed as infamous dark wizard Gellert Grindelwald – a peroxided Johnny Depp – in disguise. We last saw him being wheeled off into custody. But will he stay there? I don’t think it’s a spoiler to say no, he will not.

The new film is the first time Redmayne has returned to a character on screen. ‘When you do a play, people say, “How can you do the same show for hundreds of performances?” and the answer is that you never get it right,’ he says.

‘The endlessly frustrating thing when you do a film is that you do the scene that day, have all these ideas, then in the car on the way home you have a much better idea and there’s nothing you can do about it. Returning to a character means being able to keep bringing those ideas to the next [film]. It’s a real luxury.’

The Crimes of Grindelwald picks up roughly where the first film left off. Newt is now a famous author; Tina has returned to work as an Auror (an investigator tasked with apprehending dark wizards) and is in Paris attempting to track down Credence; Jacob is a baker (he wanted to be a baker, so that’s fine); and Queenie is desperately trying to find a way she and Jacob can be together that doesn’t break the rules against magical and non-magical people entering into relationships.

There are scenes in New York, London, and even a visit to Hogwarts, where Jude Law is introduced as a young Albus Dumbledore, but before long the whole gang are in Paris – aka Leavesden.

In the corner of a marquee that’s become a gargantuan canteen for a few months, executive producer Tim Lewis seems content enough with the arrangement. ‘Like many things, most of Paris in 1927 doesn’t exist any more, so going there now, it’s all very clean, like it had a massive jet wash. It looks lovely, but it doesn’t now look the same…’

The city of Paris ‘becomes a bit of a character’ itself in the film, reckons art director Christian Huband. He and production designer Stuart Craig – the 76-year-old triple Oscar-winner who has overseen the look of every film in the Potter universe – cheered when they saw Rowling had moved the action to Europe.

Working from photographs, drawings and animations, it gave them a chance to imagine how magic might work in not just another culture, but a different language too. The screenplay directed them, but left space for their ideas. Rowling would pop in to see what they’d come up with.

‘Jo certainly has an opinion and will wade in with it on occasions,’ Huband says, in a studio covered in miniature models and computer-drawn plans, ‘[but] she doesn’t seem to me to be the kind of writer who’s going to come in and go, “That’s not how I imagined it at all.” It’s nice.’

After making five films with Rowling, director Yates enjoys it when she challenges him. ‘It wouldn’t be fun if we didn’t have to scratch our heads to figure out how we actually deliver what Jo’s written. We have a Thestral [a magical bat-winged horse] carriage chase in this one that took months of prep and weeks of filming, combining the talents of hundreds of artists and technicians. The more complicated, the more we get excited.’

Another difficult chase involved the Parisian Ministry of Magic, the government of the French magical community, which gives us a chance to see how spellbinding bureaucracy is done in another culture. The design was inspired by the real Grand Palais, and it’s there that one of the new beasts is found. The Matagot resembles a Sphynx, and quietly gets on with menial tasks. Unless provoked, that is…

Elsewhere in the film are a Leucrotta, a massive moose with a mouth bigger than its own head; an owl-like Augurey, also known as an Irish Phoenix; and a flying lizard called a Firedrake, which can set anything flammable ablaze with its sparking tail. Almost all of them are created digitally, meaning the cast – chiefly Redmayne, as the beast-wrangler – have got used to acting opposite puppeteers controlling props with sensors on them.

‘The video-effects people on this are really like actors, because they’re my other characters in a lot of my scenes. We’re all working together,’ Redmayne says.

A portion of the set, as well as a handful of props and costumes, could be recycled from previous Warner Bros films – especially the first Fantastic Beasts (some of Paris is made from repurposed New York). For the most part, though, it was all made fresh.

Newt, for instance, has a new blue coat and a very yellow waistcoat. Costume designer Colleen Atwood, responsible for the first Oscar of the Potter universe when she won Best Achievement in Costume Design for the first Beasts film, wanted to ‘change it up a little’ and give him something brighter. She estimates that ‘over 2,000 costumes have been designed and created for the film’ (more than 32,000 man hours).

According to Yates, Depp plays Grindelwald as ‘part-visionary, politician, rock star and sociopath rolled into one’, and his costume reflects that. ‘It’s very special, and mainly dark,’ says Atwood, who has worked with Depp before. ‘It has a slight influence of lederhosen, and some things that make it quasi-Austrian.

He always has good ideas, and we have a good shorthand for costume.’ Rowling was understandably restrained in forging plot links between Fantastic Beasts and Harry Potter with the first film, instead choosing to let Beasts establish itself. This time, the connections begin to emerge, especially in the new characters.

We meet Newt’s brother, Theseus, played by Callum Turner (War & Peace), and his fiancée, Leta Lestrange (played by Zoë Kravitz) – who is, awkwardly, a childhood sweetheart of Newt’s. Amateur Rowling scholars will notice that surname: if she’s a Lestrange, she must be related to Voldemort acolyte Bellatrix from the Potter films, as well as Sirius Black and Tonks.

Like the rest of his generation, Turner, a Londoner born in 1990, read the Potter books obsessively as a child. Kravitz is only a year older but grew up in Los Angeles, raised by famous parents, Lenny Kravitz and Lisa Bonet. She was far too cool. ‘I read the first book. That’s as far as I got…’ she says, sheepishly slumping into her chair at the end of a day on set and pulling a padded jacket tight. Watford’s colder than LA. ‘I think the thing was so popular, and when something’s so popular you’re like, “I’m not going to read it.” But I think the world is very magical, and Jo’s brain and imagination are exquisite.’

Of the newcomers, it was Jude Law whose casting provoked the most headlines. He plays the young Dumbledore as a tweedy, bearded young professor at Hogwarts. ‘Jude had a pretty big pair of shoes to fill, in Richard Harris and Michael Gambon [who played the character in the Potter films], and he fills them brilliantly. He has a twinkle, a warmth, a depth and a grace that make him perfect for the younger version of the man,’ Yates says.

Initially, he admits, it was strange stepping back into the Hogwarts classroom, ‘in part because Dan [Radcliffe], Rupert [Grint] and Emma [Watson] weren’t there. And then Jude walked in as Dumbledore and I suddenly felt at home again.’

If anything in the new film doesn’t follow the lore of Potter universe, the fans will be sure to let Yates and his team know. Fortunately he cast Ezra Miller, once described by a producer as ‘our resident Harry Potter encyclopedia’, as Credence.

‘It’s true that I like Harry Potter a lot,’ Miller says, delivering the understatement of the year. He can recite whole pages from memory. ‘I’ve definitely read the books too many times, listened to the audiobooks too many times, and probably seen the films too many times. I’m also interested in esotericism, animistic practices throughout the world, and I love Tolkien, Roald Dahl, comic books… I’m a nerd.’

In Credence, Miller has arguably been handed the most interesting part of the lot. By the end of the first film it wasn’t entirely clear whether he was still alive (‘After I saw the first screening I went up to David Yates’ assistant like, “Did I get fired? Am I dead for ever?”’), but Miller was eventually reassured by Rowling. This time, Credence tries to discover his family tree and begins to understand the extent of his powers.

Miller – an intense, not-exactly-shy young American who attended a cast event for the film at Comic Con in San Diego dressed in stockings, suspenders and mushroom hat, as Mario Kart’s Toadette – describes the shoot as ‘six months of the similitude of sheer bliss and internal torture and disillusion’.

‘It’s bliss because it’s my favourite material in the world, material I’ve been deeply dependent on and ritualistically connected to since I was six years old, and with these people… and torture because Credence is a very sad boy. He occupies a space in me that is set aside just for him, his own little room, and I found this journey particularly disturbing, especially in the times in which we live,’ he says. ‘Around the time we filmed, Isis attacks happened, I was living in London thinking about Brexit and 45 [President Trump], and why people give up their power. I also found Grindelwald to be a really scary character, and his ideology to be a terrifying, transparent metaphor for the mentalities that endeavour to destroy us. [Source]