You can see it in the tell-tale orange halo at the far reaches of Silvio Berlusconi's hairline. It's there in the miraculous golden tint of Tony Blair and John McEnroe's sometime greys. It's been massaged into Michael Douglas's Donald Trump do. And then there's Paul McCartney's Heather Mills-era ginger rinse, which made such a compelling argument for divorce. The message: men, do not dye your hair. I've been going grey since university, but have never once considered colouring it, not least because the public results seem so risible. Tom Jones kicked the habit in 2008, after, he said, "I saw myself on TV and thought: 'Nah, that fucking hair!' It looks dyed, it looks false. You can't have dark brown hair when you're in your sixties."
We're always being told how good grey looks on a man: Mark Foster, Dermot Murnaghan, George Clooney. And yet, according to Josh Wood, probably Britain's premier colourist, more and more men are turning to the bottle. "We only hear about hair colour in this country if it's bad," says Wood, whose exclusive west London atelier serves both sexes. Men, he estimates, account for 15 per cent of his clientele. "I'm always asked about Paul McCartney's hair. Yes, it was coloured and yes it was bad. But there are plenty of men who you'd never know had hair colour. The secret of good hair colour for men is that it doesn't look coloured. It's taboo because nobody talks about it, because it's not meant to be talked about, because it looks natural."
Wood's female clients include Elle Macpherson, Laura Bailey, Kylie Minogue, January Jones, Jemima Khan and Sam Taylor-Wood, but he has attended to a few very famous men's heads, too, among them Mick Jagger's and David Bowie's. He was responsible for the blonde bouffant atop Aaron Taylor-Johnson, Taylor-Wood's husband, during the new film version of Anna Karenina. Most of his regular male clients, though, are "men that run huge financial institutions". Grey hair projects wisdom and experience, which is suitably reassuring on pilots and politicians – Blair and Berlusconi notwithstanding. But, says Wood, "in the entertainment industry there's a great pressure to see yourself as you've always seen yourself. And the financial sector is all about looking as on-the-ball as you possibly can."
Given the clandestine nature of men's hair colouring, Wood puts a premium on privacy and discretion. He is about to open another atelier inside the department store Liberty in central London, but his Holland Park premises is behind an unmarked black door in a quiet mews. He would never, he says, have a shopfront with a big glass window. "I have legal confidentiality agreements with some of my clients," he says. "If you go into someone's bathroom with them to do their hair every three weeks, you become part of their lives. It's not medicine, but you still have to have ethics, and if I'm privileged enough to be in that situation then I owe it to them not to write about it on my blog!"
Many of his male clients, he explains, are the husbands of his existing female clients. How does he approach a first consultation with a man? "It's very different for men and women. With women, you discuss fashion, you talk about how they're styled, what their look is. A woman walks into a salon thinking of their whole image. Most men wear trousers and a shirt, so their needs are of a different level. A woman will think nothing of bringing in a tearsheet of Gisele. I've never known a man to bring a tearsheet of anyone, not even George Clooney."
There is a unique intimacy to the relationship between Wood and his clients: these powerful men aren't trusting him merely with their hair colouring, but with the knowledge that their hair is coloured at all. He's due to travel to Moscow and Saudi Arabia after our interview, to perform maintenance on the pates of two top-flight clients. "The problem with believable hair colour is that it needs doing a lot, which is why I fly to Naples or Beijing so often. If you go to the extent of getting a colour that looks completely natural, you cannot have that tramline of grey roots. I've got clients that come in every 10 days. Generally, men who colour their hair to keep up appearances do it a lot more often than women."
Wood was born and brought up in working-class Barnsley, South Yorkshire. He "fell into" hairdressing, he recalls, after a friend of his got a Saturday job in a local salon. Wood signed up too, and was soon enrolled on a Youth Training Scheme. He saw hairdressing first and foremost, he says, as a way out of Barnsley, and before long he got a job at Vidal Sassoon in Leeds. "That was the first time I learnt that there was a difference between someone who cut hair and someone who coloured hair. I wasn't really that good at cutting and blow-drying, and there weren't that many colourists at that time – certainly not male colourists – so I thought I'd have a better chance of forging a career."
Aged 20, he left Yorkshire, and spent the next few years working for Vidal Sassoon in London and New York. In 1999, he and hairdresser Belle Cannan co-founded the Real Hair salon in Chelsea. "If I asked you to name five hairdressers, you'd immediately have Vidal, Nicky Clarke, John Frieda," he says. "If I asked you to name five colourists, you'd struggle. In this country we've always been geared towards celebrity stylists; colourists were an afterthought. If I've contributed anything, it's that I've got the colourist out of the basement."
Last year, he opened the Holland Park salon, with its staff of 24 stylists and colourists; it's breathtakingly chic, without being the least bit intimidating. (Well, maybe the least bit.) Its success has led to the in-store atelier at Liberty, which opens this month. There, too, he expects to have male clients. The recession may have made people more afraid of ageism costing them their jobs, he suggests, but, "Men's grooming has always been there. In the past, you'd have somebody to shave you every day, or to cut your hair and put oil in it."
He doesn't colour the grey in his own hair, which is spreading apace. "It's ageing," he admits. "We're not all George Clooney. But I've never really coloured to cover grey. I haven't got time for the upkeep."