Simon Price: You're not unusual, Sir Tom. You're totally unique

Ask anyone in the Vale of Glamorgan about Tom Jones, and they'll probably tell you the same story. It's the one about the time in the Nineties when the singer owned a house in Ystradowen, a well-to-do country village off the A48 near Cowbridge. Whenever he was in residence, Jones would invariably visit the local pub for a pint. The arrival at the bar of the most famous Welshman on the planet would inevitably cause a commotion, upon which he would turn around, face the patrons and good-naturedly announce: "OK, you've got 10 minutes if you want to take photos, get autographs and what have you, then please leave me be, 'cos I'm going to sit in the corner and have a drink with my friends." The villagers would, without fail, respect his privacy. He was, after all, just one of us, who'd made it big – albeit a little more tangerine in hue.

"Big", of course, is an understatement. In his 45-year recording career, Tom Jones has sold 150 million albums. If he overtakes Eminem tonight with his 39th studio album, Praise & Blame, he will be, at 70, the oldest male singer to top the charts. If he falls short, it will be only by a handful of copies. No mean achievement for a kid from the terraced streets of Treforest who was groomed for the life of a coalminer, and nearly died of tuberculosis at the age of 12.

It's easy to understand his appeal, especially to a female audience. Just look at any early photos of the sexual tornado christened Tom Woodward, taken at the time of his first forays into live performance when he was playing venues such as the Pontypridd YMCA and every working men's club in South Wales by night while scraping a living as a factory worker and builder by day. Devilishly handsome in his drainpipe trousers and Cuban heels, he looks like a Hamburg-era fifth Beatle played by a young Ryan Giggs. In those days, the young belter billed himself variously as Tommy Scott and Tiger Tom The Twisting Vocalist, with a backing band whose identity changed from The Squires to The Senators to The Playboys. He settled on the name Tom Jones after the hero of Henry Fielding's comedy novel of 1749. This simple handle stuck, although the tigerish vocalist never did stop twisting.

In the context of the early Sixties, when the mod aesthetic was on the rise, Jones – influenced by Chuck Berry and Jerry Lee Lewis, and unmistakeably a rocker – was something of an anachronism. And being Welsh didn't do a lot for his credibility. After several failed attempts to crack the London music business, including an abortive liaison with the legendary Joe Meek, Jones's career seemed to be stalling when local boy Gordon Mills spotted potential in his brickwork-rattling bellow and seismic stage presence.

It was Mills who set him up with "It's Not Unusual", an infectious song intended originally for Sandie Shaw. Released on the Decca label and featuring, as every pub quiz nerd knows, a guitar solo from the then unknown Jimmy Page, it reached No 1 on St David's Day 1965, and also broke the Billboard charts in America, where no lesser authority than Wilson Pickett described Jones as "the only white man who can sing soul".

Suddenly, Jones's anachronism was his USP. At a time when Elvis had been neutered by Colonel Tom Parker and flower-power androgyny was everywhere, Jones was a lone beacon of raw masculine sexuality. The formula worked, and the hits kept coming, along with movie themes including "What's New, Pussycat?" and "Thunderball". Cleverly, Mills started pitching Jones towards an older demographic with the maudlin country standard "The Green, Green Grass Of Home", which earned him his second No 1 single. Further smashes followed with the cheesy melodrama "Delilah" and the easy-listening monstrosity "Help Yourself", and Tom's new-found respectability earned him a transatlantic TV show.

America was calling, and Jones didn't hesitate. Relocating to Las Vegas, he became a huge draw on the casino-hotel circuit, and it was during this time that the popular image of Jones, frilly shirt naked to the waist, gyrating lewdly in leather trousers to screaming, knicker-throwing ladies of a certain age, became fixed. From a British perspective, the Seventies were Tom Jones's wilderness years, but they were also the era when he made his biggest bucks, reportedly £5m a year on the casino circuit. By 1974 he was living in Dean Martin's former Bel Air pad, and was part of the showbiz elite, befriending Elvis Presley and knocking around with Muhammad Ali.

He was also having all the sex in the world. For a man whose reputation is that of the decent, salt-of-the-earth bloke – comedian Rob Brydon does an unnervingly accurate impersonation of the singer, eagerly sincere and over-explaining everything – Tom Jones's marital situation sits awkwardly. At the age of 16, he married his childhood sweetheart Linda, and a son, Mark, was born the following month. Half a century later, Tom and Linda are still married, but his infidelities in the interim are well documented.

When she discovered he had begun an 18-month affair with Mary Wilson of The Supremes in 1968, the long-suffering Linda opted to stand by her man, telling him: "I'm not going. It would be too easy for you. But I'll cut off your balls if you carry on like this."

But carry on he did. Jones, who jokingly rationalised his conduct by telling an interviewer "marriage keeps me single; it keeps me from marrying again", would go on to enjoy a dalliance with 1973 Miss World, Marjorie Wallace. She rated him top out of her famous lovers, awarding him 9/10. George Best scored three.

In December 1990, his affair with 21-year-old Californian journalism student Cindy Montgomery became public and, most damagingly of all, in 2008 it was proven after much legal tussling and DNA testing that 20-year-old Jonathan Berkery was Jones's illegitimate son, resulting from a one-night stand with his mother, a model, while the singer was on a US tour.

His apologists tend either to sweep his indiscretions under the carpet, or to point to Linda's undoubted financial comfort (Jones's career earnings are reported to be in excess of £175m). Nevertheless, her agoraphobia is well documented: she is said to leave their Los Angeles home only rarely and has, on the few occasions that her husband brought celebrity friends home, hidden herself from view.

Jones has expressed guilt about his dalliances in his latter years, telling TV Times: "I regret I've made [Linda] unhappy.... She can't walk away from me, and I can't walk away from her."

Jones's honesty about his foibles doesn't end there. He cheerfully admits to a nose job and other plastic surgery, and that, surprise surprise, he dyed his hair for years before allowing it recently to grey. It's this lack of self-delusion and his evident appetite for performing that continue to endear him to us. A recent newspaper interview describes how, before the photoshoot, he is left alone to psych himself up for his portrait.

When he turns up on talkshows to promote his music, as he frequently does, it's hard not to be won over. Take his appearance on Jonathan Ross's sofa a few weeks ago. He was not fazed that his shirt was sopping with sweat, while happily playing stooge to Ross's patter about tight pants and baggy shirts. He barely said anything at all, and yet looked as if he was having the time of his life.

In fact, Jones's career longevity can be attributed to his happy-go-lucky approach to his image. In 1986 Gordon Mills died and Jones's son Mark took over the role of manager, masterminding an unexpected resurgence in the singer's fortunes. The following year he and the conceptual popsters The Art Of Noise had a hit with a self-parodic romp through Prince's "Kiss". Jones was rehabilitated as an icon of ironic kitsch, the leathery lothario who was willing to send himself up on chat shows, but who was also recognised – albeit belatedly – as the owner of a phenomenal soul-blues voice. Not for the first time in his life he was, truly, having it both ways.

In the Nineties, he would even receive the blessing of rock's emergent Taffia, recording with the likes of Manic Street Preachers, Stereophonics and Catatonia on the Stephen Hague-produced album Reload!. This also featured one of his finest late-period singles, his cover of Talking Heads's "Burning Down The House" with Cardigans singer Nina Persson.

Another single from the album, the Mousse T monster "Sex Bomb", was a worldwide hit, but Tom's insistence on defying the years was beginning to wear thin, and his 2002 album Mr Jones, largely recorded with Wyclef Jean of The Fugees, was a flop.

Since then, Mark Woodward and Jones himself have pursued a decidedly more dignified path. When he stopped dyeing his hair black, there was general approval, although his orange tan and white curls do leave him looking like a pint of Brains SA.

The back-to-basics Tom Jones & Jools Holland restored him to the Top 10 in 2005, and the Mark Ronson-esque retro soul sound of 2008's 24 Hours was equally well-received, if not nearly such a big-seller.

Praise & Blame is more radical still – a collection of raw blues and gospel that his label boss at Island called a "sick joke". But with its success, he's learned the lesson Johnny Cash taught all elderly artists with his American Recordings series: if you want to reach a young audience, sometimes the best way is to make the most old-fashioned music you possibly can.

In 2006, Jones was knighted for services to music, an honour which was greeted with much pride in his homeland. He may not quite have moved back to Wales, but he keeps a house there and unlike the remote, exiled Dame Shirley Bassey, he has yet to release an album under the name Sir Tom Jones. That just isn't his style. And it's another reason why Jones is still viewed fondly by the people of Wales: he's one of our own, out there, living it large.