And yet, she says, she is not good at multi-tasking. "You just hit a certain point in middle age," she says, "where you realise that you spend a lot of time worrying about how much you've got to do and it paralyses you. And you see that 20 minutes is enough to empty the washing machine, or finish a tricky final paragraph. When you have children you break the habit of being in charge of your time, and you get better at using the little bits. Oh, and I do get up very early."
The technique has obviously paid off. Over the years, Mosse has co-founded and become the honorary director of the Orange Prize for Fiction, which celebrated its 10th anniversary last year. She appears on Radio 4's Saturday Review and Open Book and BBC2's The Culture Show. And, in spare 20-minute chunks here and there, she has written Labyrinth - the novel that is about to celebrate its fourth week at the top of the best-seller charts.
"I still feel like I have to pinch myself," she says. "I've just been on a 10-day, nine-city promotional tour of America and I really just wanted to enjoy Labyrinth and not start researching my next book, Sepulchre, which is about tarot. But in LA lots of people read tarot cards, and so that was very interesting. And then when you're travelling, there is a lot of dead time and so I did a couple of book reviews, and I am working on a travel piece since I was there anyway, and also fine-tuning the Chichester festival ..."
She admits it wouldn't be possible without the support of her husband, who is the festival's co-organiser. The pair were childhood sweethearts, but met again 20 years ago at Gatwick airport in London and "fell back in love". He gallantly took her last name, but "it wasn't for political reasons", she insists. "I'm very close to my parents. His wonderful mother, who lives with us, had remarried and has a different surname. We wanted a shared name. It was a positive choice when we had children."
After the slow burn of Mosse's previous novels, Eskimo Kissing and Crucifix Lane, the mad success of Labyrinth has come as a surprise, she says. It was chosen for Richard & Judy's Book Club. The day after the programme aired, her publisher took orders for 60,000 copies. It has now been nominated for two British Book Awards in March, has sold in excess of half a million copies, and Mosse is talking to a number of companies about the film rights.
There are those who say that with this latest book, Mosse cynically set out to write a best-seller. A publisher's letter says: "Labyrinth is Kate's commercial fiction debut and as such represents a departure from her earlier, more literary novels." It couldn't be further from the truth, she says, laughing. "I think it is commercial fiction, but I didn't think my other fiction was literary." As a former publisher, she is well aware of the machinations between the writer's garret and the bookshop shelf. "It's essential for publishers and journalists and marketing and bookshops and readers to have these categories," she says, "but when it's you as an author you really don't think like that."
The categorisation of books and writing is something that Mosse has struggled with for at least 10 years. When the Orange Prize was launched to promote fiction by women, she says she was taken aback by the negativity of some of the reactions. "I thought people would be celebrating," she recalls. "But some of the press was very aggressive."
In the years that followed, Mosse cajoled, bossed and flirted women's literature on to the agenda. "I don't think women write differently," she says. "I think all authors write differently. In Labyrinth, for example, I wanted to write about women's place in the Crusades. So I write from a woman's point of view. But writers like Beryl Bainbridge, Iris Murdoch and Zadie Smith have a big interest in the male perspective."
Last year, for the 10th anniversary of the Orange Prize, Woman's Hour contacted 20 people who had spoken very vocally against it at the start. None agreed to appear on the programme. "People ask, if the Orange Prize has succeeded, then why is it still necessary?" she says. "As long as there are people all over the world who are being told about books they otherwise wouldn't read, it will go on."
Every year, the organisation puts money into research and literacy projects. It has produced reading guides to help teachers encourage boys to read. Most important for Mosse, it has led more people to read.
"For some people, winning a prize is about the honour," she says. "I'm more pragmatic. The important thing about prizes is that they get books more readers."
"Female authors are always asked whether the success will make a difference financially," she points out. "Helen Dunmore got quite fed up and said, 'Would you say that to a man?' I admit, when I came back from America I went into a bookshop and I looked at my book under a big No 1 sign. And my children looked at it. And it was lovely. But you just don't go around thinking in those terms. You think, 'I've got to give a speech at a library tomorrow. And I've got to research the next book. And I've still got to do the Hoovering before the end of the day.'"
A look of fierce determination came over Alaïs. 'With respect, Paire, there is even more reason to let us go. If we don't, the books will be trapped within the Ciutat. That cannot be what you want.' She paused. He made no answer. 'After everything you and Simeon and Esclarmonde have sacrificed, all the years of hiding, keeping the books safe, only to fail at the last.'
'What happened in Besièrs will not happen here,' he said firmly. 'Carcassona can withstand the siege. It will withstand. The books will be safer kept here.'
Alaïs stretched across the table and took his hand.
'I beseech you, do not go back on your word.'
'Arèst, Alaïs,' he said sharply. 'We do not know where the army is. Already, the tragedy that has befallen Besièrs is old news. Several days have passed since these events took place, even though they are fresh to us. An advance guard might already be within striking distance of the Ciutat. If I let you go, I would be signing your death warrant.'
'I forbid it. It is too dangerous.'
'I am prepared to take the risk.'
'No, Alaïs,' he shouted, fear fuelling his temper. 'I will not sacrifice you. The duty is mine, not yours.'
'Then come with me,' she cried. 'Tonight. Let's take the books and go, now, while still there is the chance.'
'It is too dangerous,' he repeated stubbornly.
'Do you think I do not know that? Yes, it may be that our journey will end at the point of a French sword. But surely it is better to die in the trying, than let fear of what may come to pass take our courage from us?'
To her surprise, frustration also, he smiled. 'Your spirit does you credit, Filha,' he said, although he sounded defeated. 'But the books stay within the Ciutat.'
Alaïs stared at him, aghast, then turned and ran out of the room.
From 'Labyrinth', by Kate Mosse, published by Orion (£7.99 paperback)Reuse content