SHE complains that her memory is fading, she can't work a computer and the Internet is a complete mystery to her - yet best-selling novelist Jilly Cooper is still as sharp as a knife when it comes to her powers of observation.

The author, who made her name with riotous tales of sex and scandal among the upper classes, laments that she loses things, can't remember what she has written half an hour before and is probably out of touch with the world.

The day we meet, she struggles through the door of the west London house she bought for cash from the proceeds of her novel Polo, armed with a large Russell & Bromley bag and some goodies for her newborn grandson, Lysander - named after Lysander Hawkley, the dashing hero of her blockbuster, The Man Who Made Husbands Jealous.

Jilly may be nearing 70, but she's sparkling company - mischievous, clever and uplifting, just like her books.

''I still don't know how to text or work computers. I work on a manual typewriter. I've only just got a mobile phone and I turn it off because if a call comes in it unnerves me. But I did have two calls this morning which I managed to answer, so I'm progressing.''

The house has become the home of her adopted daughter, Emily, her husband and their two young children, on whom grandmother Jilly clearly dotes.

It has taken four years for Jilly to complete her latest novel, Wicked!, a tale of class differences as a posh independent school offers to share its facilities with a sink comprehensive.

It may sound heavy, but Jilly has created a fatally attractive headmaster and a headstrong, pretty headmistress, along with a wonderful cast of children. She even finds a place for the dashing, heart-meltingly handsome cad Rupert Campbell-Black in her story.

The book runs to a staggering 848 pages and for that she spent more than two years visiting both independent and state schools, talking to teachers, pupils, heads and support staff.

"Teachers are strangled by serpentine coils of red tape," she says. "Why not just let them teach? I did masses of research, only because I'm so out of touch."

Her own two adopted children, Felix and Emily, went to state and private schools. Jilly admits she was quite laissez faire about their education.

"I was shocked when Felix went to this prep school and suddenly I was told, 'Mrs Cooper, Felix isn't doing his homework'. I said, 'What homework?'.

"They obviously thought I was a bad mother. Then Emily got suspended three times from Cheltenham College for smoking in the loo, drinking at lunchtime and then driving a boy around without a licence.

"I don't know why I was so irresponsible. I suppose the idea was that if you were paying for education, the teachers should get on with it."

While she was working on Wicked!, her daughter got married and started a family, Jilly spent a lot of time fund-raising for the charity Animals In War and, most devastatingly, Leo, her husband of 45 years, was diagnosed with Parkinson's Disease.

"I don't think we took it in to begin with,'' she recalls. "He was suddenly very slow at getting dressed. He shook a bit but he doesn't shake at all now because he's got some medicine. It breaks my heart because he's so brave and so jaunty."

She has had some emotional storms to brave in her life, too. When she discovered that Leo had had a six-year affair, she didn't air her dirty linen in public. She later said: "An affair can happen to anybody. I don't think it's a reason for a marriage to break up."

She also admitted that she had had an affair in their early years of marriage, for which Leo forgave her.

How have they managed to weather the storm?

"It's creaking bedsprings, and that's from laughter rather than sex," she says.

The couple live in a a pretty village near Stroud, in Gloucestershire - neighbours include Liz Hurley and Ruby Wax - where Jilly writes her saucy tales and cares for a menagerie of animals.

Jilly admits she is finding it much harder to write as she gets older.

"The awful thing with the latest book is I would think, 'God, what did I say half an hour ago?' - that's the awful thing about old age. You do not remember what you said two minutes ago."

Sex is not as prevalent in Wicked! as in some of her other books, although that wasn't planned, she says.

"I just toddle along and suddenly it seems a nice time for two people to go to bed together,'' she says cheerily. ''But everything has got much more respectable.

"My generation wasn't into condoms and I couldn't have children anyway. My young copy editor got very hot under the collar and said, 'Really, you've got to have some condoms here'. I said, 'When? What type? And at what moment do you put them on?'"

She's already started the next novel, The Village Horse, about a grandmother in a Cotswold village who breaks away from her selfish family to look after a mistreated racehorse.

So retirement and a quiet life in the Cotswolds isn't on the cards, then? "Not a chance!"

* Wicked! by Jilly Cooper (Bantam, £17.99