Alan Titchmarsh: The call of the mild

He is the BBC's great white hope. A broadcaster of such stature that he is being talked about as the next David Attenborough. Or Simon Schama. Or possibly both. Who could this televisual colossus be? Some chisel-featured Oxbridge academic groomed for stardom? No, it is a 5ft 9in, squeaky-voiced, self-styled potting-shed sex-god who was the inspiration for Steve Coogan's character, Alan Partridge. Step forward, Alan Titchmarsh: your days as the man with the spade, as the foil for Charlie Dimmock's water features (and other attributes) are over.

The 52-year-old multi-millionaire expert on clematis wilt is abandoning Ground Force and Gardeners' World for a far higher calling. He is to present a BBC documentary series on British flora and fauna, aimed at doing for natural history what Schama's A History of Britain did for knights in armour.

Corporation chiefs believe Titchmarsh, winner of the Literary Review Bad Sex award and legend in his own pullover, has the "respect and gravitas" to rank alongside his hero, the popularly known "Whispering Attenbore". And, it is rumoured, his Ground Force co-stars are not too happy about it.

Not that this will be Titchmarsh's debut in the world of highbrow television, of course. There was the celebrated time he interviewed Nelson Mandela, who, returning from a trip to see President Clinton in the US, found that the garden at his retirement home in Qunu, South Africa, had been Ground Force'd while he'd been away.

Never having heard of the programme – or even Titchmarsh himself, God forbid – the octogenarian world statesman was only just able to conceal his horror at the hastily erected maze of rose arbours and water features better suited to suburban Surrey than the hot, dry terrain of the eastern Cape.

As a result of this BBC voyage into the surreal, viewers prepared themselves to see the Dalai Lama's home given the makeover treatment on Changing Rooms or perhaps Saddam Hussein's Baghdad palace become the deserved next victim of the Ground Force team.

But Titchmarsh has long fancied his chances outside the herbaceous border. For 10 years he had his own show, Pebble Mill at One, where he interviewed everyone from Placido Domingo to Julia Roberts. All very capable it was too, but when the programme came to its natural end no one missed it, or least of all Titchmarsh himself.

A horticulturist by trade, he found himself back in the obscure backyard that was gardening TV until Ground Force came along in 1997 and changed everything. It was, however, rookie broadcaster Charlie Dimmock's tiny T-shirts and cavalier approach to underwear that allowed the show to blossom from BBC2 obscurity to prime-time BBC1 glory. Television lore has it that Titchmarsh's rather large nose was put out of joint by Dimmock's extraordinary popularity, as he was used to being the "natural" in front of the camera. But along the way he also acquired the unlikely status of pin-up, having twice been voted as the second sexiest man in the world after George Clooney and then David Beckham.

Titchmarsh, who got through nearly half a century without attracting much interest from the opposite sex, now found himself mobbed by women at the garden shows of Britain. And his admirers were not all middle-aged biddies thrilled by his sensitive handling of tomatoes. Young women have also fallen for his coy looks up to camera while declaring love for a plant's "large, creamy bracts".

Revelling in his new role, Titchy, as he was known at school, has become Teasy to the growing numbers of women who see gardening as a substitute for sex – or perhaps confuse the two. On a recent episode of his other new series, How to Be a Gardener, he thrilled millions when he cooed: "I'm just going to snip and release this," while fumbling with the ties of a tethered wisteria as if they were the clasps of a bra. And when the wisteria fell, willingly, into his hands he whispered: "You can almost hear her going 'Oooh!'."

Although happily married for 26 years to Alison, whom he met at the Richmond and Barnes Operatic Society, Titchmarsh is clearly only too pleased to discover that Madame Tussaud's regularly has to clean the lipstick off his wax model.

His fervent imagination has served him well in his alternative career as the author of slushy, romantic novels packed with sexual escapades of the wholesome bronzed bodies and clean, white fluffy bathrobe sort. He won the Bad Sex award for this passage in Mr MacGregor: "She planted moist, hot kisses all over his body. Beads of sweat began to appear on Guy's forehead as he became more entangled in the lissom limbs of this human boa constrictor."

Rugged, broad-chested muscular heroes, no doubt dab hands with their marrows, frequently display their "tender" side in a formula that appeals to the same sort of woman who goes weak at the knees over his television appearances.

All four of his novels – there are two more in the pipeline – have been bestsellers, further adding to the considerable Titchmarsh coffers, which are also boosted by more than 40 gardening books, newspaper columns and personal appearances. Home is a rambling house in Hertfordshire with 30 acres. He built a 60-seat theatre next to it for him and his wife to stage entertainments for their friends as well as productions in aid of charity; he also keeps a 38ft trawler yacht in Chichester. A holiday place on the Isle of Wight and a Mazda sports car complete the rich man's trappings.

It's all a far cry from school in Ilkley, West Yorkshire, where, dismissed by his teachers as a no-hoper, he left at 15 with a single O-level in art. His father was a plumber, but both his grandfather and great-grandfather had been professional gardeners and he had inherited their green fingers, building his first polythene greenhouse when he was 12.

His first job, at Ilkley Parks Department, was a revelation to Titchmarsh, and he knew immediately he belonged to the earthy world of foliage and compost. A prestigious apprenticeship at Kew Gardens followed, and then a stint on various horticultural magazines.

He got his lucky break in 1979 when the BBC magazine programme Nationwide sent him to report on a plague of greenfly in Margate. He shone on camera and was soon snapped up by the BBC to do gardening spots for Breakfast Time before moving on up to Pebble Mill.

To describe him as the Delia Smith of horticulture is to underestimate the Titchmarsh factor. Saint Delia sets off runs on omelette pans, cranberries and sea salt after a casual commendation on air. But Titchy wiped out the nation's stocks of flowering onions – otherwise known as alliums – after singing their praises in his TV review of the Chelsea Flower Show, which he had also made into a spectacular ratings success. And gardening – apparently we spend more than £3bn a year on it – has overtaken cooking, DIY and even football as the nation's favourite pastime.

A recent poll placed him as the seventh most liked and respected person in Britain, after Dame Judi Dench, the Queen and Professor Stephen Hawking, and ahead of Prince William, Sir Paul McCartney and David Beckham. It seems that not even his decision to play Gordon Gnome – who shares a wheelbarrow with a worm called Andrew – in a new children's TV show can topple him from his lofty perch. Now the "titch" from Ilkley who became the unlikely king of makeover TV is being groomed for even greater glory. Arise Sir Alan? Who would bet against it?