It will be one of the biggest rock concerts of the year, but as Coldplay take to the stage for their massive Wembley stadium gig on Saturday, there will be one pair of Bristolians watching the show with pride.

The epic stage – which will stretch for the full width of the new Wembley pitch – will largely comprise a series of enormous screens. Throughout the show the screens will display the work of art designers Jason Mullings and Paul Tigwell, and their team of Bristol-based graphic artists.

All in all, the pair have come a long way since they set up their art design business Hello Charlie five years ago, with nothing more than a pair of laptops in the kitchen of their Kingsdown flat.

These days, they enjoy the rather more swanky surroundings of a Berkeley Square office, overlooking Park Row and the Wills Memorial Tower.

In recent years the pair have worked with stadium rock bands like The Who and Queen, and created television credit sequences for shows such as The Brits, Casualty, Gordon Ramsay's The F Word and most recently, Jamie Oliver's American Road Trip.

"We were tremendously lucky very early on when we were given a commission to work on a screen sequence for Britney Spears," Jason says.

"We had a number of contacts within the industry, because we'd previously worked at the BBC in Bristol. We tried to put the word out that we were setting ourselves up in business, and somehow our work was seen by Britney's management, and before we knew it we were offered the commission.

"It nearly went terribly wrong though," he adds. "The night before I was due to fly out to the States to present the work, our hard drive seized up, and we very nearly lost the entire project.

"Thankfully a computer engineer was able to retrieve the work just in time for me to jump on to the plane. But at that point our career could have been over before it had really begun."

Things are rather more sophisticated these days. The Hello Charlie offices are awash with Apple Mac computers and white designer meeting tables. The name of the business, incidentally, is a nod to a famous line in The Italian Job – the Michael Caine movie that has become a design classic in its own right.

"We now have a permanent staff of 10 people – ranging from illustrators to animators," Paul explains. "But we also have a similar number of freelancers that we can pull in when the big projects are at their height."

A flick through the Hello Charlie portfolio reads like a Who's Who of the entertainment industry – they've worked with the likes of Roger Moore, Ewan McGregor, Claudia Schiffer and David Beckham on Unicef adverts, and Robbie Williams on a number of TV documentaries.

But for Jason and Paul, the Coldplay gig has to be one of their biggest projects to date.

"All the band members and their art director Phil Harvey have been great to work with," Jason says. "They asked us to create a series of visual backdrops for the show – a different one for each song. They left everything up to us, so we went off and worked on ideas, and then came back to them with about 30 or 40 different pieces. Some are animations, but some are short films.

"There isn't an over-arching theme as such, because we've tried to tie each piece in with the corresponding song, but there is a recurring imagery of space and planets."

Paul adds: "It can be a difficult balance. You don't want to create a music video, which the audience will watch as if they're in the cinema, while ignoring the artists on stage. The visuals on the screen have to compliment the band's performance."

Paul and Jason have plenty of experience with this emerging art form – having worked on similar live show screen visuals for Muse, Kaiser Chiefs, The Who, Franz Ferdinand, Queen and The Ting Tings.

"We did a sequence for James Blunt's performance at the Brit Awards in 2006, which extended the music video for You're Beautiful," Jason says.

"At the end of the video, we see James jumping off a cliff. So we took the story up from there, and filmed James in the water, alongside a synchronised swimmer.

"It's great when you can take an artist's work and move it on in another direction.

"It's always exciting to be part of that process."