David Marshall has an irreverent sense of humour, casual demeanour and enthusiasm for exercise and it’s hard to know which of these qualities keep the celebrity clients banging at his door. Certainly, the low-key setting for his private gym in a nondescript north London street gives no clue to the stars that are sweating right inside it.

‘There are a lot of people in the public eye who come to us – some serious superstars,’ he explains ‘But no one will ever know who they are. Even the people who live in the street don’t know this gym exists.’

Although he’s tight-lipped about most of his high-profile clientele, plenty have publicly sung his praises – including stars of The Mummy Returns Racher Weisz and PatriciaVelazquez, TV presenter Dani Behr, model Sophie Dahl, Faye Tozer from Steps, former Ballykissangel actress DervIa Kirwan and celebrity hairdressers Daniel Galvin Jnr and Nicky Clarke. He’s also put multi-million pound footballers Rio Ferdinand and David Ginola through their paces, as well as the whole West Ham United Premier League team.

‘They all pay their money, never miss their appointment and are up for the same late cancellation charges as anyone else,’ he says. ‘They don’t ask for favouritism and, in return, I’ll never take a ride on anyone’s back.’

But privacy is just one of the reasons he’s the trainer that singers, actors, TV presenters, models and sports people turn to when they have to shape up and slim down in an impossibly short period of time.

David, who began his current profession almost 27 years ago when a serious knee injury ended his dreams of professional football, teaches just one training regime to every client, regardless of gender, age or fitness.

He works to a mantra that the body is a whole and that stressing it with intense workouts and the wrong foods leaves it unbalanced.

His ideas have drawn sniggers from many in the fitness industry, but hundreds of testimonials from those who’ve rigidly stuck to his intensive six-week programme all suggest he’s on to something.

‘Our principles are derided by virtually everyone in the fitness business and we get laughed at. But I think that’s fantastic,’ he says with a cheeky grin. And judging by the accolades from his celebrity clients, David’s obviously on the right track.

‘I’ve been telling all of my friends about David,’ says Steps singer Faye Tozer, who admits she’s thrilled with the transformation in her figure after training with him. Faye and her boyfriend Jasper first started David’s programme with just six weeks to get fit for the British 10K, a charity race held in London on 22 July.

‘I didn’t expect I’d be able to run the whole way, but Jasper stuck by me and we did it together in just 1 hour and 2 minutes,’ she told NOW.

‘David’s programme was amazing and I’m definitely going to keep going. I’ve been amazed by the changes in my figure already. The back of my legs and bum look amazing. I’m proud to be seen in my bikini now!

‘And Jasper looks absolutely fantastic,’ she adds with a giggle. ‘He’s got these sexy; toned arms and a nice stomach.’

Former Ballykissangel star DervIa Kirwan also turned to David after agreeing to compete in the same charity race.

‘If I hadn’t been training with him, I’d never have been able to run that far,’ she confessed to NOW . ‘He’s been phenomenal, absolutely brilliant. I’ve never run a race before in my life and not only did I make it the whole 1Okm, but I did it in just 51 minutes.

‘There’s no question that I’ll keep training with him. I’ve lived in gyms for the last 10 years and he’s the best trainer I’ve ever come across. I’ve dropped two dress sizes in six weeks. I’ll hold my hands up and admit it’s simple old female vanity, but I’m so happy with how I’m looking.’

Latin American actress Patricia Velazquez, who starred alongside Rachel Weisz as her scantily-clad rival in The Mummy Returns, first met David on set, where he was official trainer to the cast.

‘Never has my body looked so good, my whole shape has changed,’ she says. ‘Now I’m back in New York, I’m doing all of the routines from the book and it seems to be working.’

The programme

‘Basically, most women want to be sculpted, toned and in proportion,’ says David. ‘So the kind of work we do lends itself to giving someone a swimmer’s physique with low body fat and long, lean, flat muscles.’ For this to happen, it’s the quality of exercise done and not the quantity that matters, he says.

David starts all of his clients on the same six week regime: three 90 minute sessions each week, which include a 15 minute warm up, 55 minutes bodywork (weights and abdominals), capped off with a 20 minute cardio (aerobic) workout.

Going against conventional gym law, he shuns the usual ‘three sets of 10’ and instead revs up his clients to do one long set.

Drawing on the principles of yoga, the 90 minute session is done in a specific sequence so that each new exercise stretches out the muscles used in the last one. This, he says, should leave you more flexible after the session than before.

He also hands his clients a relatively strict nutritional programme which blacklists wheat, non?organic dairy and processed food, warns against combining protein and starch in the same meal and recommends eating carbohydrates in the meal before working out (for energy) and protein in the meal afterward (to replace lost muscle protein).

For more information: contact Bodydoctor fitness on 020 7235 2211, fax on 020 7586 6892, e-mail to info@bodydoctor.com or visit the website www.bodydoctor.com.