Styles' video for

Treat People with Kindness came out on New Year's Day - though it was shot in London in February 2020.

Choreographer Roberts had worked often with Styles in the One Direction years. Roberts says the timing of the shoot, at the art deco Troxy in Stepney, east London, turned out to be fortuitous.

"We had a great time but we didn't know how lucky we were. Looking back it was about three weeks before the world started to burn. Maybe that's partly why people are loving it now - the video has such a carefree sense to it."

Roberts has had 20 years as one of the UK's most in-demand commercial choreographers. He created dances for the 2019 Spice World tour and has worked with everyone from Katy Perry to Sir Paul McCartney.

He devised work for the dance group BalletBoyz and, as well as stage work, he choreographed One Direction in videos such as Kiss You, Steal My Girl and Best Song Ever.

"So when Harry got in touch to say he wanted me for a new video it was a thrill. The only definite thing was it would be a song from the album Fine Line - but we didn't even know which song would be chosen."

With One Direction, Roberts spent six years working with a hugely successful boy band whose members insisted dance would never become a major part of the act.

Wasn't that a choreographer's nightmare?

"It was always really interesting working with One Direction. I knew very early on that there was a magic about them and I could see they had other skill-sets aside from being this very good-looking five-piece - and then four-piece - band.

"In personal moments you got to see them flourish. They'd mess around doing silly dance moves but I'd think, 'Actually if you wanted to dance really well you sure as hell could do it.'

"So when Harry contacted me and we spoke about doing a video with a lot of dance I was like, 'Well I've been waiting 10 years for this.'" Styles knew he wanted Phoebe Waller-Bridge to have an equal presence.

"I believe Harry went to see Phoebe in the West End when she had her success with Fleabag. They went out to dinner and got on really well. That's when Harry started to think how they could work together in some way."

Before shooting began there was a five-week rehearsal period - far more generous than most projects ever get. But a lot of the time Styles and Waller-Bridge weren't in the same room or indeed country.

"I was with Harry in a dance studio in London and we had all kinds of music to try out from modern alternative stuff to old school big band and Glenn Miller. We were exploring. Only on the third day did we begin to apply what we'd done specifically to the Treat People With Kindness track.

"Meanwhile Phoebe was in Canada working on the James Bond script. But fortunately I had a brilliant assistant on the project called Jared Hageman so Jared flew out to work with Phoebe. And eventually Harry needed to be in LA so I went there.

"He was amazingly devoted to the whole thing. He'd be shooting the Watermelon Sugar promo in Malibu and they'd wrap at 8pm but he'd get in a car and come to the studio and we'd rehearse moves until gone midnight."

Roberts says by then it was clear the choreography would at least nod to the Hollywood of an earlier age.

"The directors Ben and Gabe Turner sent me a link to a black and white movie from 1943 called Stormy Weather. There is a justly famous sequence in it with the Nicholas Brothers, Fayard and Harold, called Jumpin' Jive.

"I think it's the greatest dance-sequence ever filmed and Gabe and Ben and Harry all wanted our video to have some of the same feel.

"I think in Harry's head he wanted to push himself to the absolute limit of what he was capable of. We were never talking about just an average soft-shoe shuffle.

"So the reality was that I and Jared would talk constantly and exchange material from thousands of miles part. And of course Phoebe and Harry would also pitch in ideas.

"We wanted to find a dance language that would take things as far as we could possibly go with Phoebe and Harry, without it becoming comedic.

"Actually my big worry was practical - that they'd both start out with massive energy but that as the weeks progressed you'd have these two incredibly busy people with no time for everything needed to make the project special. But neither would give up, not for a moment."

He says it was important the dancing had a contemporary edge as well. "Harry and Phoebe are modern artists and very intelligent. They're fashion forward-thinking.

"I find that once you've stopped giving artists their steps it's often quite nice to step back and just watch how they interpret the music. Sometimes little gems can be grabbed and put into the mix.

"It was discovered very early on that both Harry and Phoebe had huge potential. The delight came from their energy combined with the talent of the film-makers plus the extended period of time we had to rehearse.

"I work in a world where budgets have shrunk considerably so it was a big investment for managements and Harry's label."

Roberts remembers the two stars finally came together for little more than the last week of the project, including the shoot. But there was still time to bring in a ballet dancer to give guidance on "port de bras" - how to hold your shoulders or extend an arm gracefully.

"Harry and Phoebe are both decent and generous beings. So we all kept it fun, despite the blood, sweat and tears which had gone into the preparation.

"When finally we were together they could layer on little side-eyed glances or maybe some tiny movement of the face which the camera would pick up. Above all we wanted a sense of style [no pun intended] and panache."

He says the fact most of us feel a real lack of either style or panache in our lives has given Treat People With Kindness an impact as a video it might not otherwise have had.

"The whole thing has a nostalgia for a time where you could be in a club and socialise with friends with no social distancing. I think the chemistry Harry and Phoebe have together just oozes joy. And for most people joy is in short supply."