Keeping his head

By contrast, their co- star Head sat on the sofa, calmly sipping a drink and chatting to me without batting an eyelid. He was as cool as an ice cube in an eskimo's fridge.

And he still is today. The star of the most famous coffee adverts in history possesses a smooth un-ruffled-ness that draws the eye and creates a rare magnetic aura.

It has also – it has to be said – turned him into a huge sex symbol. It is no surprise to learn that the star of Buffy the Vampire Slayer was once voted "the sexiest man in sci-fi". He seems entirely at home in the so-hip-it-hurts atmosphere of the ridiculously trendy central London vodka bar where we meet. As he walks in, sporting shades, a killer all-black outfit and an earring that glints at me from the lobe of his left ear, I half-expect to hear This Charming Man by The Smiths come through the sound system.

With typical wryness, however, Head laughs off the heartthrob tag. He looks a good decade younger than his 54 years, but he roundly dismisses the idea that his legions of female fans would like nothing better than to watch him in love scenes. "No-one would be interested," he scoffs. "In fact, I've only been asked to do love scenes at a time when it's not quite as interesting as it might have been once. I seem to be taking my clothes off much more of late, which is not necessarily a good thing. One time, it was definitely for comedy. But no, nobody's asked me to do porn."

Fame and fortune have clearly not gone to Head's head. In fact, he adopts the sort of refreshingly irreverent outlook that is not always prevalent in an industry whose motto might as well be "Narcissists Are Us." The actor – who has been happily living with his partner, a horse-whisperer called Sarah Fisher, for more than 20 years, and is the proud father of two teenage daughters, Emily and Daisy – cheerily concedes that he is a little bit on the wacky side. "Oh yeah! But healthily. Of course I'm nuts. Hopefully, most of us are. If we take ourselves too seriously, then we'll disappear up our own orifices."

That doesn't stop Head being recognised a great deal. But he takes it all in good grace; in fact, he grins as he admits that "friends often ask me, 'do you ever get bored with people coming up and asking for autographs?', and I reply, 'it's going to be much worse when it stops!'"

Thanks to Buffy the Vampire Slayer, the American sci-fi series which – even five years after its demise – continues to inspire fanatical devotion, Head has a global following and has been waylaid in the most unlikely places. "I'm still recognised all over the world," reveals the actor, who was born in Camden, north London.

"But the strangest occasion has got to be when I was approached by the security guard at a morgue in Bucharest. I was there to film a series entitled True Horror for the Discovery Channel. A criminal pathologist had just shown me what happens to a body after death and how it could be interpreted as a sign of vampirism. It is one of the most unpleasant memories I have! I was still reeling from all those cadavers when the security guard sidled up to me and said, 'I love Buffy the Vampire Slayer. Please sign this!' It was sweet – it had taken him all morning to pluck up the courage. But I was still unnerved because he looked exactly like Boris Karloff!"

The slightly unsettling fans aside, Head is clearly enjoying life. "This job is a joy," he enthuses. "You feel like you're paid to have fun. Oops, I better not say that – producers might complain!"

There is a fine-wine bouquet about the actor, who has flourished during his middle years. "The older I've got, the better things have become and the more high-quality roles I've been offered. Maybe producers trust me more now – the fools!"

He has now been trusted with the joint lead in The Invisibles, a likeable, larky new BBC1 comedy drama about a couple of ageing likely lads, Maurice (Head) and Syd (Warren Clarke), growing old disgracefully. In this series, which starts at 9pm on Thursday, they leave the Costa del Crime in order to laze around at a retirement home in a sleepy Devon village. But the tranquillity of retirement doesn't suit them – in fact, it drives them up the wall. Maurice, in particular, is deeply depressed by the fact that his flat boasts an alarm he has seen advertised by Thora Hird. Before you can say "Ronnie Biggs" they are up their old tricks and pulling off blinding blags once again.

There is a touch of Minder about the series – perhaps it is no coincidence that it was penned by William Ivory, who started life as a writer on the well-loved Arthur Daley series. Head emphasises that Maurice and Syd are not baddies, merely loveable rogues. "Ultimately, they are good people – or perhaps they're two halves of one good person. They commit crimes, but high-end crimes. They're modern-day Raffleses, class villains who are never violent and they only rob those who can afford it."

They also refuse to go gentle into that good night. "The Invisibles deals with a number of issues we all face as we get into our fifties," muses Head. "We start to look at who we are and where we want to go from here and what we have achieved. For Maurice and Syd, that hinges on their success as criminals. As they get older, they are supposed to come to terms with their fallibility, but Maurice kicks against that. He takes the idea of retirement personally. He still wants the adrenalin rush of doing jobs. What would he do without that?" Acting was always in Head's blood. His mother, Helen Shingler, played Maigret's wife in the classic 1960s TV series; his father was a television director and his older brother, Murray, was one corner of the love triangle (the other two were Peter Finch and Glenda Jackson) in the classic 1971 movie Sunday, Bloody Sunday.

After studying at the London Academy of Music and Dramatic Arts, Head first made an impact more than 20 years ago in a series of Gold Blend TV advertisements that became iconic of the Thatcherite era. He displays no embarrassment now about the series, which ran for almost a decade and showed a yuppie couple (Head and Sharon Maughan) going gooey-eyed over the instant coffee. "Why would I? The Gold Blend thing gave me a good old wad, which meant that I didn't have to do stuff I didn't want to do. From that moment on, I've been really fortunate."

The actor, who owns a lovely house in Somerset, says he took on the adverts "because it was an interesting project. It was. It was. It was. It was very well done and, ultimately, it was no different from doing a soap. It was just the fact that we recorded only two a year."

While no doubt lucrative, the campaign may have stalled his TV career for a while. According to Head, "I don't think I was tainted by it, but my agent did say someone had told him, 'this is a serious drama. We don't want people reaching for their coffee jars'." But, fortunately, the ads never held him back in the States – quite the reverse. They were so popular there that the actor was cast in the career-transforming role of Rupert Giles: school librarian by day, Buffy the Vampire Slayer's Watcher by night.

After the worldwide success of that show, Head had his pick of parts. He chose to play another well-loved fictional role, the charismatic Prime Minister stalked by his predatory gay assistant, Sebastian (David Walliams), in Little Britain.

But the actor reveals that he almost turned the role down. "I really wavered about it," recollects Head, a decent singer who was once in a band called Two Way. "When they sent me the script for the BBC3 pilot, there were four Prime Minister sketches, and on paper they all seemed quite bald. The gag was 'Sebastian fancies the Prime Minister' four times over. I didn't quite get the tone. But my agent was adamant and said, 'the radio show's brilliant. You're doing it!'"

It was a good decision. "Once I started rehearsing with Matt and David, it was immediately funny. They are lovely guys and very open to ideas. They're not in any way precious about their own work. When we got it in front of an audience, my jaw dropped. Matt and David's performances were so outrageous and out-there. I thought, 'either this will be pilloried or people will love it'." We all know now which way public opinion went.

In the meantime, Head has another authority figure to tackle. In BBC1's forthcoming new teatime drama, Merlin, he plays Uther, the dictatorial king who bans magic in Arthurian times. "I'm giving my king," the actor smiles. "Why is this a good time to revisit Merlin? It's always a good time to revisit Merlin. Myths are legends are so open to re-interpretation. This is Smallville Meets Camelot."

Like Maurice, his alter ego in The Invisibles, Head can't kick the adrenalin rush of work. He will have to be dragged kicking and screaming from his job. "I want to go doing this for ever," he beams, as he pops on the shades once more and prepares to leave. "I can't imagine ever saying, 'right, that's it, I've had enough now'. I'll go on acting till I drop."

A HEAD FOR DRAMA

Nescafe Gold Blend commercials, 1987-1993

IN the late 1980s, Head appeared in a series of 12 television advertisements for Nescafe Gold Blend, with the actress Sharon Maughan. These ads were like a mini-soap, based on unresolved sexual tension, with the dewy-eyed couple exchanging flirtations but never quite getting it together. The ads were inexplicably popular, with an astonishing 30 million viewers tuning in for the "will they, won't they?" denouement in 1989. (And yes, they did.)

Buffy the Vampire Slayer, 1997-2003

Head played bumbling school librarian Rupert Giles in the cult television series for five years, assisting Sarah-Michelle Gellar's Buffy in the relentless battle between good (attractive teenagers) and evil (blood-sucking vampires, also attractive). The role gained him international recognition, but he eventually left the US show to spend more time with his family in Britain.

Monarch of the Glen, 2004

Head guest-starred in several episodes of the popular Scottish Sunday-night drama in 2004. He played Essex charmer Chester, who, having made his fortune in poultry, moved to Scotland and caused trouble in the Glen by setting his sights on Isobel (played by Simone Lahbib), much to the annoyance of his love rival, Paul.

Little Britain 2003-2006

One of the best-loved guests in the popular comedy sketch show, Head played the charismatic Prime Minister, Michael, completely oblivious to the lust directed at him by his aide, Sebastian. The sketches featured some of the most memorable moments in the show, including a passionate man-on-man snog between Head and David Walliams, who played Sebastian.

The Invisibles starts on BBC1 at 9pm on Thursday.