Sir Roderic Llewellyn Bt, better known for his high-society bedfellows, has a new business venture — and a more wholesome and decent business venture it would be hard to conjure. He is holding a series of one-day seminars on “the basics of gardening”, in this case at a newly built, faux-period mansion near Shipston-on-Stour, Warwickshire, just up the road from the cottage where he lives with his wife, Tatiana.

On the day I tip up, seven exceptionally pleasant-looking ladies of a certain age are in attendance, all of whom have coughed up £95 for the privilege.

It might seem a lot, but the price includes lunch in the dining room — white wine, chicken with tarragon and sundry related dainties.

Also present on the day are Tatiana, who looks intelligent and friendly, and bustles in and out making coffee for everyone, and another woman, elegantly dressed, called Fudge Ramsay. Ramsay has lent Llewellyn her house, her Emma Bridgewater coffee mugs and her smart dining room; in exchange, Llewellyn is donating 10% of all the proceeds from the seminars to Ramsay’s favourite charity, Shipston Home Nursing.

We are sitting in a pleasant circle, the ladies and I, in what looks like a large conservatory. There’s an astonishingly handsome gardener roaming around outside, but sadly he has nothing to do with the occasion, which is, of course, staggeringly, magnificently, breathtakingly respectable.

And why shouldn’t it be? After all, Llewellyn has an impressive horticultural career behind him; a career inspired, he tells us, when at the age of three, “Nanny” introduced him to a packet of seeds and a tulip bulb.

“Very unimportant event, of course,” he says, standing before us all in his amusing yellow braces. “But there you have it. I watched them grow and I thought it was a complete miracle. Sort of sparked off the idea . . . of a career . . . So I’m very lucky.”

Since then, of course, among other things, Llewellyn has published no fewer than seven books on the subject of gardening. He has been gardening correspondent of several national newspapers. He has presented innumerable television shows about gardening, as well as being the gardening presenter for This Morning with Richard & Judy.

He has designed gardens around the world. He has designed an entire range of garden furniture. He has lectured on gardening matters as far afield as Sydney. He has acted as chairman at garden lectures and been the patron of garden charities. In fact, my God, this man shouldn’t be called Sir Roderic Llewellyn Bt at all, he should called Sir Roderic the most productive and expert gardener in the history of the entire universe Bt.

It’s all very well, though, isn’t it? Llewellyn could have written a million books on gardening. He could have single-handedly hung all the gardens of Babylon, but the question is: did he or didn’t he have it off with Nicky Haslam?

And if he did, who was more fun in the sack? Haslam, the Peter Pan of interior design, with whom Llewellyn, as a young man, shared a basement flat in Fulham for a year? Or HRH the late Princess Margaret Rose? He and Princess Margaret were at it for eight long years, of course (as any tabloid reader from the 1970s would be able to tell you). Even so, longevity isn’t everything, is it? I think I can guess. Poor Margaret Rose.

Unfortunately, Llewellyn has long since moved on and doesn’t want to talk about all that stuff — as has been made clear in the invitation I’ve been sent. “Throughout the workshops Roddy will be delighted to answer delegates’ questions,” it reads, “but strictly on the subject of horticulture only!”

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