The past is another country. I wrote things differently there. First it was the school day: O-levels, A-levels. I was always writing. Some paint, some play an instrument, some swim fast, some run. I wrote: poems, plays, stories – anything, so long as it was words on paper. During O-levels I started a novel, because I asked advice from the writer Pamela Hansford Johnson, who told me I should.

When I left school, writing had to be fitted around work as a book reviewer for a newspaper. I wrote early morning and late at night, in sample notebooks given by a neighbour who worked “in stationery”.

I started to write all day when I was sacked from the Coventry Telegraph, an incoming editor not caring for books. I had a £500 loan from a bank manager who took a punt on my becoming rich and famous. He wanted no interest, only a signed copy of the eventual novel. Was ever a bank manager such a fairy godfather?

Several novels came after that, written in great bursts, every day, all day, when I rented a house in Suffolk overlooking the North Sea. I did my best work during those few years, writing by hand, still, then typing up. The novels were shortlisted for, and won, prizes. I was still in my 20s. Slowly, the backlist grew.

A personal tragedy, three years in the wilderness, and another novel, written at white heat, often all night, in six weeks. I needed no schedule. I ate, slept, walked by the sea, wrote. Days went by when I spoke to no one. It was a focused time.

But then came marriage, domesticity and a child, followed by a long, desperate quest to have another. More tragedy, before a final gift of the gods, and another baby. I was out of the writing game. I had no interest in writing, no energy, no emotional space. I thought I had given up for good and said so.

But unlike for the athlete or the ballet dancer, age is of no consequence to the writer. When I was 40, and my eldest child five, I felt a tension within me which I recognised, belatedly, as the need to write again. I had had my gap years. I was still a wife and mother, but time had expanded while I wasn’t looking.

Facebook Twitter Pinterest A production of The Woman in Black at the Fortune theatre, London. Photograph: Martin Godwin/The Guardian

For six weeks, someone looked after my daughter every morning. I had to write a book. And I did. The Woman in Black, for fun, really, to see if I could. It was nothing like any I had written before and it was fun. It wrote itself.

Since then, there have been no more long gaps between books. I am 75. My daughters are adults. I am a grandmother. Time stretches ahead. Or does it? “At my back, I always hear ... ”

Writers die but they never retire. I no longer have time pressure. No exam looming, no school pickup. I can write as I like, when I like, and I do. Mornings – not often. Afternoons – sometimes. Evenings, and late nights. Yes. Weekends. Yes, if I want to. I have no office. No room of my own. Kitchen table. Sitting room sofa. Bed with mounds of pillows. An hour. Two. No long days. There are places to go, things to see. Coffee shops. Dog to be walked on empty beaches under wide skies. Family to see. Twitterers to follow. Something of everything. The best way.

I am rebuked. Can I be a serious writer, keeping such casual hours?

Maybe I am not. The books are all very different from each other now. I challenge myself. Ghost stories. Crime. Literary fiction. Non-fiction. That does not sound like proper professional writing either. Whatever. My 59th book, From the Heart, is a novella and as serious as I can get. It comes from a writer without a schedule, office or desk, who still writes by hand.

But a writer, all the same. I had better be. I am unemployable otherwise.

• From the Heart is published by Chatto on 2 March. To order a copy for £9.34 (RRP £10.99) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.