Bestselling author Joanna Trollope may be 64, but she's not too old to go nightclubbing. In fact, she graced some of Britain's hottest nightspots as part of the research for her latest novel, Friday Nights, which features a budding female DJ. House was her music of choice.

Once branded the queen of the Aga saga, her books include The Rector's Wife, Other People's Children and Second Honeymoon. She said: "Clubbing for anybody over 30 looks like an impenetrably peculiar thing to want to do, but I wanted to get under the skin of it to make the character credible."

She met Tabitha Denholm, half of the Queens Of Noize and an-ex girlfriend of Pete Doherty, but later found another DJ for her research. She ended up going to Neighbourhood, a popular nightclub in London. "There were these two huge black guys on the door. I wore black, put my specs on, took my notebook and a big friend. Whatever anybody was thinking, Nobody said, 'What is someone your age doing in here?' They understood the research was serious. I didn't dance but I stayed for three or four hours talking to people all the time. The kids, aged between about 16-25, were like puppies - round me all the time asking what I was doing and would I send their mum a copy of the book.

"I've got the mobile numbers from all these Darrens and Eds and Sophies and Emmas who were saying, 'We'll take you to a real club. This is quite tame'. It was fascinating."

The book centres on a group of women who meet every Friday night in the home of Eleanor, a retired professional. When one member starts dating a man, it throws out the group dynamics, testing the strength of their friendships.

Trollope's acute powers of observation and her ability to reveal complexities in relationships feature in all her novels. Despite the 'Aga saga' label, they are often quite bleak, tackling difficult and uncomfortable problems.

She is a clever writer, but also immensely accessible; she provides an easy read but you don't come out feeling like you've gone through 300 pages of fluff.

Some of the material she uses to tackle major personal issues such as marriage, adoption and stepchildren - which have been the focus of previous novels - is inevitably based on personal experience.

Trollope herself has been twice-divorced, having left her first husband for her second. She went through a mini-breakdown when she later broke up with him. Today, she is happily single and lives alone in London. She has a large family, including her two children, two stepchildren and seven grandchildren.

Tall, thin and elegant with a plum-in-the-mouth accent, she's a confident woman who certainly doesn't give the appearance of being lonely.

A distant descendant of Anthony Trollope, she was born in the Cotswolds and grew up in Surrey, gaining a place at Oxford University. She began writing "to fill the long spaces after the children had gone to bed" and for many years continued working as a teacher. She became a full-time writer in 1980, but it wasn't until her fourth novel, The Rector's Wife, that she hit the big time.

Friday Nights explores female friendships, a subject she has touched on in previous books.

"In the playground, little girls are pretty horrible to each other. Then there's adolescence, where your friends are everything, because that's the way of getting away from your ghastly, embarrassing family.

"Then there's this extraordinary period of your fertile years, when you have these passionate best friendships but the opportunities for sabotage are so great and your physiology and particularly fertility make women quite treacherous to one another if you drop a man in the mix.

"Then you come out to the best bit of female friendship when the competition for men really is not relevant any more and you begin to choose a really eclectic group of friends, a lot of whom you wouldn't introduce to each other."

She is aware of the complications that can arise when a man comes between female friends.

"I remember episodes when people regarded as very close friends came on to my boyfriends - or to my first husband, in one case. You just think, 'Where do your loyalties lie, sister?'. I didn't have the nerve to say anything at the time but now I wouldn't stand any of that nonsense. I was shocked - and afraid that I didn't have the power to hold on to either of them.

"I've had female friends disapprove of my choice of men but I've never had a female friendship broken by a man, although I've seen it happen."

When she left her first husband, banker David Potter, for her second husband, playwright and screenwriter Ian Curteis, she doesn't recall losing any of her female friends. "One said, 'I wish I'd got the courage to leave. I'm actually rather jealous of what you're doing'. But all the others were extremely supportive because they understood that I wasn't leaving the perfect situation."

For a while, after she split up from Curteis and was single again, she was seen as a predator by by some wives, she reflects. "I did notice a tremendous anxiety among married women. I almost thought of having a sign printed saying, 'You cannot imagine how much I don't want your husband'."

Now, she says: "I have at last got to a place where I very much like being."

She says she wouldn't want to settle down again and then pauses: "Well, you say, 'No,' and then, of course, there may come along a miraculous person who would change your mind in which case everything I've said would go out of the window. But as things stand, I can't imagine it being an improvement."

And she doesn't get lonely, she says.

"The loneliness that's inherent in a relationship which has gone wrong is so much worse than the loneliness of being on your own. A great deal is made of loneliness in modern society and unless you can come to terms with your own company I don't think you really are ever going to achieve contentment."

Nightclubbing may not be at the top of her agenda as she gets older, but books still are. She already has the outline for another novel, and her seven grandchildren keep her busy.

"There are so many plusses to being over 60 - the liberation of it. Society has an unspoken rule book for how women should be at each age. By the time you get to 60, society has lost interest and there's a wonderful freedom. It gives a kind of confidence now which is a great relief after all those anxious decades."

Friday Nights is published by Bloomsbury at £18.99.