Joanna Trollope in high spirits

“It was on sale for three days and went in straight at number one,” she says jubilantly. “This has never happened to me in all this time, over this long career. I’m thrilled! I couldn’t pretend that I feel any other way.”

Trollope, 66, is about as bankable a novelist as any publisher could hope for. Since her breakthrough success The Rector’s Wife, in 1993, almost all her books — tales of domestic strife set in some idyllic, genteel patch of England — have enjoyed phenomenal sales, but her latest does seem to have achieved a new high watermark for the perennially popular authoress.

Not only this, but the book has also been garnering universal praise from the critics.

“That’s a first as well,” she said. “Again, I don’t know what’s happened. Maybe this book is more on the pulse than others. Or they do all just like it better. I don’t know. I’m stunned and grateful.”

So, high sales and high praise for her most recent literary offering. No wonder a note of giddiness beneath her cut-glass vowels and her otherwise polished demeanour.

The truth, of course, is that Joanna Trollope, bestselling novelist and distant relation of Anthony, has always delighted and deterred in equal measure; her tales of middle-class anguish are incredibly popular but they have generally provoked mixed feelings amongst critics.

"I feel really blessed in terms of my readers," she says. "I’ve had incredible loyalty from them. Bless their hearts, they have seemed to be rather bad-review-proof."

She seems acutely mindful of the fact that she might, sometimes, have shortcomings as an author. Indeed, the impression is of a refreshingly modest novelist. She says that ‘vulnerability is an important part of the creative process’.

“If a review is bad and it’s personal and vitriolic and I’ve never met the person, then I don’t really take that very seriously,” she said.

“But if it’s an adverse review that is intelligently written, then I think that’s really on the writer’s side. It is saying: ‘come on, you’ve let yourself down’.”

Of course, she’s been plagued by that ever-present epithet Queen of the Aga Saga, since author and journalist Terence Blacker coined it back in the early nineties.

"It’s so patronising to my readers,” she said, emitting a rueful sigh. “It suggests they are only capable of reading something very shallow and unsatisfactory.”

All in all, though, Trollope seems to have a clear-eyed view of her own work.

She writes about the ‘human fears and joys that we are all familiar with’, giving them a contemporary context, and does so in a deliberately simple style.

“There is nothing new to write about,” she said. “There is no new subject that Shakespeare or Sophocles hasn’t covered already. I don’t believe in writers as great prophets; I believe that we are interpreters. Our task is to reinterpret old human truths afresh for our own times."

Trollope was an English teacher for 12 years before becoming a professional writer (at first, she wrote historical fiction under the pseudonym Caroline Harvey, before turning her attention to contemporary fiction). She has read a great deal since childhood, but her eyes were fully opened to the wonders of English literature at Oxford, where she studied in the early sixties.

Did Oxford shape her in crucial ways?

“Oh yes, when I got to Oxford, it was the first time anyone had asked my opinion about anything intellectual,” she said.

“It was an enormous period of intellectual confidence, a period for satisfying my intellectual curiosity.”

She smiles as she recalls the advice offered to her by Kathleen Kenyon, the renowned archaeologist who was principal of her then all-female college, St Hugh’s.

“She said, ‘I’m not going to discourage you from falling in love but try not to domesticate your relationships. This time at Oxford is your last chance not to be in charge of domestic life. So, for goodness sake, don’t cook for men and don’t do their laundry. Just have love affairs.’ When you look at it, it was extremely modern advice.”

Although Trollope has had homes in Gloucestershire and London, where she now lives, she also had a recent spell of living in Oxford (one of her daughters, a barrister, still lives here).

“I had a go at living in Oxford but actually I think to live in the city you have either got to be part of the university or have a young family, because the whole place is so education-orientated," she said. “You need a kind of entrée into that world.”

She returns to Oxford on March 21, to discuss her latest book at the Oxford Literary Festival. She sounds peppy about appearing at the festival, partly because it will be an opportunity to discuss her relationship with the city where she found her ‘intellectual confidence’. It was in Oxford, after all, that she learned to develop her views about literature and the role it plays in everyday lives.

She said: “We all love stories but, actually, our own story is the most absorbing of all. From the outside, our lives can seem rather normal and humdrum, but, living them, they feel like the last act of Hamlet.”

Twice married and divorced, Trollope has two daughters from her first marriage to banker David Potter, whom she married aged 22, and two stepsons from her second.

The author admits that when writing The Other Family, she knew what it was like to have the jumbled emotions which pervade the minds of so many of her characters.

She said: “I think one of the most desperate things in life, which I was trying to portray in this novel, was that however much you say you want a marriage to work, you cannot make the other person commit the way you do.

While in her mid-30s, Trollope met TV playwright Ian Curteis. That relationship eventually spelled the end of her marriage and her subsequent divorce coincided with a 'mini-breakdown' and a spell in therapy.

“Of course [marriage] should be a partnership, but sometimes you simply cannot make the other person participate and understand. I try and portray these disappointments because I think they happen everywhere and I think a lot of people are striving to do the right thing and it really isn't their fault when it doesn't work.”

The Other Family, her 15th contemporary novel, tackles the subject of inheritance and the ripples that are created when musician Richie Rossiter, a crooner from the Eighties, dies, leaving his current family emotionally drained and his previous wife and son in a tangled mess over his legacy.

Matters are further complicated because Richie never married his current partner Chrissie, with whom he had three daughters.

“There's an enormous preoccupation with inheritance," said Trollope.

“Inheritance laws are so inequitable between married people and those who are co-habiting.

“When I was thinking about this, everywhere I looked, every newspaper, every magazine, seemed to be thinking about it.

“It got me thinking that those who are left behind after somebody has died are rather inclined to measure how much they are loved by how much they are left.”

She says she gains her ideas from reading the papers, talking to friends, riding on buses and trains where she can eavesdrop on conversations and simply sitting in cafes watching the world go by.

In her latest novel, Richie leaves his beloved Steinway piano to his first wife and son, which forces contact between them and the woman he left them for.

In her own life, Trollope and Curteis left their partners to be together, but eventually divorced. She admits that when her first marriage collapsed, she wasn't equipped to deal with the emotional turmoil.

“There's no dress rehearsal for these things. I'm not the kind of person who would have done such a thing on a whim. I got to the point of feeling that I was going to be not just distorted but destroyed by the situation I was in. But, you know, my children came with me.

“It is difficult to get things right,” she reflects. “You make choices that you hope will last. I think if you marry very young there's a 50:50 chance that you'll grow apart.

“One of the secrets of not going mad is realising that you can change yourself and you can change your situation, but you cannot change other people.”

The book also serves as a warning to women who rely on men too much for their money and their future.

“My friend Susan Hill (the author) always says, sagely, women should never let go of their friends or their money because they never know when they'll need either. I think that's very sound advice.

“When you look at girls now who are looking for a man who will keep them, that's a very dangerous surrender. If you are going to be kept by somebody there's inevitably a price to pay for it.”

Today, Trollope is still extremely close to both her daughters and her two stepsons, who are now in their 40s, while her first husband remains a friend.

She also has nine grandchildren, on whom she dotes.

• The Other Family is published by Doubleday. Joanna Trollope will be appearing at the Oxford Literary Festival on Sunday, March 21.