WCXX

An unlikely small-screen celebrity, Keppel had been glued to Millionaire from the moment it began. She had never taken part in a quiz before, but was short of money and decided to give it a go.

"I noticed the questions weren't that difficult and the prize money was huge. I wasn't aiming for the million; I thought £32,000 would be nice." Keppel, now 71, told no one except her children when she was accepted on to the programme (her family was "astonished, slightly embarrassed, amazed and, in the end, very pleased that I'd won"), and she was petrified to find herself in the spotlight next to Tarrant, having won the "fastest finger first" round (putting four former prime ministers in the correct chronological order).

"Once it started it was less terrifying because the lighting ensures you can't see the faces of the audience, for obvious reasons — so they can't mouth the answers," she remembers. "And the good thing is it's over very quickly — I didn't have time to think about the money because I was focused on the questions."

Keppel answered 15 multiple-choice questions to reach the jackpot, using up all her "lifelines" — ask the audience, 50/50 and phone a friend — on the way. The £1 million question was which king was married to Eleanor of Aquitaine. When Tarrant announced she had got it right, Keppel smiled, but failed to faint dead away, kiss the host passionately or even break open the bubbly (having given up alcohol around the time of the break-up of her first marriage in 1980).

Disappointed by her apparent stoicism, the tabloids promptly christened Keppel, the granddaughter of the 9th Earl of Albemarle and distant cousin of the Duchess of Cornwall, "Posh Dosh" and described her as too rich and po-faced to deserve her winnings. But Keppel says that was not the case: she was simply too stunned.

"It seemed completely unreal," she says. "The thing is I'd be concentrating on holding myself together for such a long time that when it came to the end, I couldn't suddenly let go and be excited. I wasn't a very good contestant for them because I should have burst into tears and screamed. But I couldn't."

While not on the breadline, Keppel says she had been struggling for money before she went on Millionaire. Divorced twice (she was previously married to art dealer Desmond Corcoran, with whom she has three children, and scriptwriter Neil Shand), she lived on a fixed income from investments. "They never seemed to keep up with inflation," she sighs. She was also unsuccessfully trying to set up a garden design business, "but none of my family are any good at business whatsoever; it was much safer to stay out of it".

Since her win, she has appointed a financial adviser, sold her Fulham house and bought a property in Albi, south-west France, near friends, and a small London flat; she has also enjoyed a couple of exotic holidays to India and Laos. "I suppose I felt a bit freer when I went into a clothes shop or a shoe shop," says Keppel. "It was a lovely feeling being able to relax."

But Millionaire helped her beyond the first million; her success meant that she compiled quizzes for The Daily Telegraph, wrote a book of her own and was recruited as a team member on the BBC's Eggheads, which pits former quiz champions against amateur teams. She has been doing that for a decade now, and her earnings mean that she has not touched the capital of her original winnings.

Unlike her fellow Eggheads, however, she does not spend her weekends going to endless quiz championships. "They take those kind of things much more seriously. Eggheads is just a game to me, and it's lovely," she says. "It means I live in London in the winter, because we film Eggheads in the autumn and in spring, and then I spend half the year in France which is heaven. My family come out to stay, and I revise for Eggheads there, and just … live.

"It was very easy to move. I just woke up one day and thought, 'I don't want to moulder away and die in London, I'd like an adventure'."

She is discreet on the subject of her famous cousin, but says they met again recently in Glasgow when the Duchess of Cornwall went to the BBC studios while Keppel was filming. "I have seen her since then, I wouldn't say I know her well — but we know enough to say hello and recognise each other." For those who want to emulate Keppel, to what does she attribute her success?

"Well, I've no idea what makes me a good quizzer. I think I have a quirk in my memory that means I remember trivial things easily. For Millionaire I didn't do any revision because I thought it would scramble my brain, but I do for Eggheads. I read the Telegraph's sports section every day because sport is my downfall."

But a vital ingredient for women, she believes strongly, is to be single. "I've always thought I wouldn't have done Millionaire if I'd been married," she says. "I just feel my husband would have said something like, 'Don't be so silly', and then I wouldn't have done it. And I think there are a lot of women out there in similar situations who maybe don't have the confidence to go on TV. It's a real shame."

She will be glued to the last episode of Millionaire, a celebrity version starring Sir Chris Hoy, the Olympic cyclist, and Rachel Riley, the Countdown presenter and Strictly Come Dancing contestant.

The show's audience has been shrinking — by June last year it had fewer than 2.3 million viewers — and Tarrant has commented that, post-recession, "as a nation we've stopped gambling" (as well as that "we're running out of celebrities with a brain cell" to take part).

Yet for Keppel, it still represents the perfect recipe for a compelling quiz show: multiple-choice questions; playing one contestant at a time; the psychological pressure the show exerts; and, most of all, the big money on offer.

"I feel very sad to see Millionaire end because it gave me such an amazing opportunity," she muses. "And I'm rather surprised, because I don't know why people don't still want to win a million. After all, we could all do with it."

Š'Celebrity Who Wants To Be A Millionaire?' will be broadcast on Tuesday at 8pm. 'Who Wants To Be A Millionaire? Chris's Final Answer!' will be shown on Feb 11 at 8pm, both on ITV