When Mark Ronson and Lily Allen decided to work together, the results were always going to be special. The duo's cover of the Kaiser Chiefs' Oh My God is set to be one of the feel-good hits of the summer, and now thanks to Nima Nourizadeh, there's a stonking promo to match.

Nourizadeh has worked with Allen twice before, on the videos for LDN and Littlest Things. But this time the set-up is a little bit different: the pop princess may be known for her colourful behaviour, but now thanks to some technical wizardry, he has coaxed her into producing her most animated performance to date - quite literally.

The video begins with Ronson apparently working alone in his studio, late at night. He fingers a mysterious card on his desk - one bearing a suggestive pink silhouette. Suddenly we see him hurrying down a dark alleyway to the door of a seedy-looking nightclub. The bouncer lets him in, and he moves past a midget magician and down into the bowels of the building. As he enters the main room, the houselights dim and the chattering crowds fall silent. The main act is about to begin.

As the red velvet curtains part, Lily Allen appears - in cartoon form. The ensuing show pays gleeful homage to the film Who Framed Roger Rabbit, as the sassy singer teases her enraptured audience, cartoon and reality seamlessly meshing together. One young punter attempts to film her on his phone, but Lily pushes him aside with a deftly-swung leg; at another moment, she plucks a drink from a waitress and sets it down in front of the Kaiser Chiefs (making a guest appearance in the video for their song) before sucking the glass dry through a straw.

Only Ronson seems able to keep his cool in Lily's presence, and for this she rewards him with a rose, and the card from the clip's beginning. The action cuts back to the studio, and the cartoon Lily emerges from the sound booth with a "Was that alright, Mark?".

Nourizadeh explains that Lily Allen's busy schedule prevented her from taking part in the clip, and this provided the perfect opportunity to realise one of his long-term concepts. "It was an idea I'd had in my head for a long time," he reveals. "In fact I'd spoken to her about it once before. As soon as I heard the track and I knew Lily couldn't be in it, I knew that this was the right time."

While he was writing the pitch, Sasha Nixon, executive producer at Partizan, put the director in touch with a French illustrator named Fafi. "Her stuff is really amazing - cute but also quite sexual as well, with a really great look to her characters," explains Nourizadeh. "We thought it would be really nice to get her involved."

So Fafi came to London, where she drew up initial character sketches for Partizan's in-house animators. This initiated a lengthy creative period that involved work on both sides of the Channel. "It was a really long process, because there was so much going back-and-forth," says the director. "There was someone in Paris building the model and sending me images, and we had to fiddle with skin tone, hairstyle and all that kind of thing. We could start the animation of the character, how she moved, and then re-apply changes to the model, so it didn't hold us back - the only thing we couldn't change was the body's proportions."

Once the design was complete, Nourizadeh and his team shifted their attentions to the live-action scenes. The entire club sequence was shot in one day at a working men's club in New Cross, and the notable absence of the clip's cartoon star meant a high degree of prescience was needed at all times. Both Fafi herself and editor Leo Scott attended the shoot to ensure everything went as planned, the former working with Lily's stand-in to help her move "in character", the latter checking that individual shots would fit into the tight constraints of the final cut.

It goes without saying that nailing the right camera angles and movements was only half the battle. The crew still had to contend with the task of getting their invisible cartoon star to interact with solid, real-life objects, and unlike the makers of Who Framed Roger Rabbit, who had access to expensive, cutting-edge equipment of the time, Nourizadeh and his team had to improvise:

"We had a couple of contraptions we used," the director reveals. "You know those litter-picker things with the gripping tongs? We used that to pick up the glass off the tray. And the old fishing wire trick, that always works! In fact, the hard part was keeping everyone's eyelines on the subject. The thing that really helped was the spotlight we used - it gave people a reference, something to follow."

Meanwhile the scene where Lily sucks up her drink required the use of a half-metre-long straw, with animation producer Isabella Parish on the end of it. That was par for the course on a shoot where everyone wanted to get involved - the Kaiser Chiefs even took an early flight back from Austria so that they could make their cameo appearance. Aside from the Kaiser Chiefs, eagle-eyed viewers (and music video insiders) may have spotted some well-known faces among the cast of the video: Ronson's band are in the audience, while directors Kinga Burza and Anthony Dickenson show up respectively as the waitress and the seedy camera-phone fan.

"The night before the shoot I was round Mark's place, and he said his band wanted to be in it," explains Nourizadeh. "With Kinga, I said 'I need a cute barmaid' and she was like, 'cool I'm up for it.' And then with Anthony, I called and said 'I need a pervert' and he was like, 'cool, man!' He was funny, I thought he made a very good pervert!"

With the design of the star and live-action shoot complete, all that remained was to unite the two elements - a task undertaken in three gruelling weeks. "It was really intense - loads of all-nighters," says Nourizadeh. "It was a job that should require a month to five weeks, but we only had about half that. We had a big team of animators, and I found that quite difficult - you constantly need to be communicating with them, and them with you, so when you multiply that by 12 people, headaches happen really quickly!"

Despite the cerebral pain, Nourizadeh is rightly very proud of the final clip, and one of the distinctive features of this music video is that it's the first where all the animation was done in-house at Partizan Lab, the production house's new animation wing. "They really pulled it out of the bag for me," he concludes. "With the time and the money we had, it would have been an impossibility if we'd gone elsewhere. It's one of those things where if we'd had more time it might have been a bit different, but in the end we did the best we could and I am really happy with it."