So what is it about Hugh Grant that you find particularly insufferable? It is a debate that inspires such passion it could keep the Commons up for an all-night sitting, but for me it can be answered in two words — Jemima Khan — so overwhelming is my jealousy. How could she, of all girls, be snaffled by Grant? Let’s just look at the score card. She is one of the world’s most beautiful women and among the most glamorous: confidante of Princess Diana, ex-wife of Imran Khan and one of only five Britons on last week’s Vanity Fair list of the world’s best-dressed swells.

Oh, and for those who find bank vaults sexy, she also rubs pashminas with the richest (her father was Jimmy Goldsmith, the late billionaire who squandered a few spare millions on the Referendum party). And yet Jemima fell for that bumbling cad who always plays Hugh Grant in any movie he appears in.

There is a late scare that our meeting will be cancelled. A helper announces that Jemima is “flat-out busy”. Doing what, she does not explain. While I wait I reflect bitterly on those recent tabloid photos of Jemima wrapped around Hugh in the Caribbean. Perhaps that’s what the helper means by busy. Cattish critics might say that Jemima is a kind of upmarket Liz Hurley (that earlier Grant squeeze) who, though a lovely, intelligent adornment to national life, does not have anything quite so vulgar as, well, a career to keep her occupied.

Luckily Jemima manages to squeeze me into her busy schedule after all. I tell male friends casually I am off to meet Jemima (it works a treat), but I remember the Roxy Music refrain: with every goddess a let-down.

Not our Jemima. She arrives (eventually), model-thin in tight jeans and black jumper with designer holes at the shoulders, exposing a hint of sun-kissed skin. At 31 she is as ravishing as ever, though there is darkness under her piercing brown eyes — a hangover, perhaps, from her recent divorce from Imran, the Pakistani cricket captain turned political voice in the wilderness.

To fill the void in her life, like many privileged women, she has turned to charitable endeavour. But unlike ladies who throw the odd luncheon for a teddy bear appeal, Khan devotes herself to Unicef’s campaign against Third World child poverty. If her father was an unacceptable face of capitalism she is a more than acceptable face of compassion.

Comparison with a certain other glamorous, high-born English blonde is inevitable, but my suggestion of her being the new Lady Di is met with her withering stare. “I wouldn’t compare myself to Princess Diana; that would be very presumptuous, I have to say.” But the comparison is not as outlandish as all that: Khan has that Diana quality of sounding regal yet empathetic, friendly yet reserved — and just that little bit lost, too. There is much in the world she finds “shocking”, uttered in perfect vowels through perfect lips.

Sometimes when a celebrity endorses a charity, the real charity case is the faded star showered with much-needed coverage. Not Khan. She has no single/fitness video/cable chat show to promote. We meet on sufferance as she loathes the media; and after a paparazzo snapped her consummating her marriage on a hotel balcony, who can blame her? The rules of the interview could not be tougher if Ali Campbell were moonlighting as her spin doctor — the mere mention of Hugh, whom she has already denied she is about to marry, warrants a red card.

Above all, for the most desirable heiress of her generation to leave London for Lahore as she did aged 21 in 1995, and to remain for nearly a decade, suggests one moved by matters more profound than photo ops. And unlike the boy band plugging the children’s charity, who were unable to say what the charity did, she has done her homework, reading reports and visiting disaster areas. Indeed, she knows more about Third World disaster areas than she seems to know about modern Britain.

(Ironically, her marriage started to go wrong when she returned to Britain to do a master’s degree in Middle Eastern politics.) “I haven’t lived in England for much of the past nine years,” she says by way of explanation. Despite her divorce she says she still intends to spend a considerable amount of her time in Pakistan. “I still feel a real connection with Pakistan, with my children being half Pakistani. I spent so much time there I almost feel as though I grew up there.” In some ways she probably did.

Indeed, she is retaining the name “Khan” as “I want to have the same name as my children.”Some speculate she was miserable in Lahore, missing out on the fast life in London. “Well, I came and went, so I didn’t entirely cut myself off.” But she must have felt schizophrenic changing costumes in the first-class loos? “I got very used to it. In the beginning I found it more difficult coming back to England than going to Pakistan.”

Really, why? “Just relating to my friends who were doing such totally different things, but that was more to do with my lifestyle: aged 24 I was already married with two children.”

Part of the time she intends to spend in Pakistan in the future she will devote to her business. She employs local women to embroider clothes she hopes to flog in London (traditional Pakistani embroidery is “no longer fashionable in Pakistan” while the ethnic look is pretty hot here).