He produced his second, Pointless Nostalgic, a year after graduating, in 2002.

Cullum’s unique vocal style and treatment of jazz standards and popular classics by artists as diverse as Miles Davis and Jimi Hendrix soon caught the attention of audiences and music critics throughout the world and led to Universal signing him for a £1m record deal in 2003. He insists his fame was hard-earned. While studying English at Reading he was also working as a singer-pianist at nights in pubs, hotels and wedding receptions to help pay his way.

“I didn’t think I had the talent, confidence or ability,” he says. “I made albums and sold them after gigs. I didn’t think any more about it.” His older brother Ben was a primary influence on Cullum’s career and plays electric bass on some of his albums and co-writes with him.

Prince William is a fan of Cullum’s music and in February GQ magazine voted him 139th in its list of the 200 most powerful men in the world. An extravagant-sounding claim, perhaps, but the magazine was making a point about the influence of his music.

Cars have been integral to his success, allowing him to tour the country from his home in rural Wiltshire in the early days. “I started driving as soon as I could,” says Cullum, whose parents met while working at Ford’s plant in Dagenham, London. Cullum was born in Essex but the family later moved to Wiltshire. “I wanted to be independent, especially as we lived in the countryside. I had my first driving lesson on my 17th birthday and passed my test first time.”

His first car was a Vauxhall Corsa, which cost him £1,500, paid from his savings. “My dad got a good deal on it through his contacts. It was a basic model with no radio or cassette player. However, I fitted one a few weeks later. The bodywork wasn’t too bad, apart from the colour, which was bright green. It didn’t go very fast, but it was mechanically sound, which was more important for getting me to gigs.”

Over the years he has owned a succession of cheap and practical motors, including a Fiat Punto and a Mitsubishi Colt Space Star. “The Mitsubishi was great for carrying my keyboard and PA system and was reliable, comfortable and very economical on petrol. I slept in it many times and sold it about six months ago.”

Today Cullum can afford to drive slightly more luxurious cars. He is sponsored by Audi and gets the pick of the marque’s range of executive cruisers. “I drove an Audi TT for a while, but required a bigger car, so they gave me an Audi A4 quattro. It’s really comfortable and great to drive. I love all the gadgetry.”

However, these days he doesn’t need to drive himself to concerts: he gets chauffeured by car and tour bus instead, or occasionally by public transport. “It’s not always practical to take my car and public transport is just as good. It’s also cheap and eco-friendly,” says Cullum. “I used to drive to concerts years ago and was clocking up thousands of miles a year. Now all I use the car for is to drive to the supermarket and to my parents’ home in Bath.”

One thing incenses him about driving — speed cameras. “I hate speed cameras. I think they are a bloody nuisance and cause more accidents by making people brake suddenly. That said, I don’t drive fast and I try and keep to the speed limit. I grew up in a village where most of the deaths were caused by people driving too fast.”

Driving in America, where his album Twentysomething was nominated for a Grammy, is a different experience entirely. In Los Angeles he got to drive an open-top Cadillac. “It was great fun to drive, especially on such wide open roads,” he says, adding that other road users are not quite so considerate as those in Britain. “A limousine drove past me with its back windows down. I glanced over and saw this couple having sex in the back. It’s hardly something you expect to see in public, never mind on the highway in broad daylight!” Despite his new-found wealth and the fact that the days of driving himself to concerts all around the country are over there is a sense that Cullum still hasn’t forgotten those early days of living out of the back of his car, driving from gig to gig. “I remember I had finished a gig late one night and was feeling really tired,” he says. “Rather than take a nap I got into my car and drove off.

“As I was driving down a motorway, I started to nod off and woke up just as the car was heading towards the central reservation. Fortunately I braked in time and managed to control the situation. It really freaked me out and I stopped at the next service station for several hours to recover from the shock. Since then I never drive if I’m tired and always stop for a break.”

His dream car, then and now, is a VW camper, forever associated with carefree hippiedom and surfing. “A mobile home on wheels is all I really want,” he says.

ON HIS CD CHANGER

I love most types of music: Sufjan Stevens’s Come on Feel the Illinoise, Late Registration by Kanye West, and Apologies to the Queen Mary by Wolf Parade. I also like Sander Kleinenberg and Miles Davis. I listen to TalkSport, Radio 4 and Gilles Peterson on Radio 1

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