Legal judgments are an extraordinary sub-genre of our literary heritage, says acclaimed novelist Ian McEwan.

Five years ago, Sir Alan Ward, a judge in the Court of Appeal, told Ian McEwan the story of a case he had presided over, involving a young Jehovah’s Witness and blood transfusion.

‘As he was telling me, I thought there was a short novel in this,’ McEwan recalls. ‘So I consigned it to a notebook. [Sir Alan Ward] referred to it again some time later, which revived my interest. I was just as intrigued then as I was when I first heard it.’

After hearing about the Jehovah’s Witness case and ‘reading about a handful of parallel cases’, McEwan was fascinated by how ‘these cases really devolved into an issue of the secular sense of what was justice and what was religious’.

That fascination led to The Children Act, which is published tomorrow. The novel centres around Fiona Maye, a leading High Court judge. While dealing with her own marital problems, she is called upon to hear an emergency case involving a 17-year-old boy who, because of his religious beliefs, is refusing medical treatment that could save his life.

Over the years McEwan has become interested in judgments, ‘bad ones as well as good’. He describes them as a ‘quite extraordinary and neglected sub-genre of our literary heritage’.

Did writing the book affect McEwan’s views on the family court? ‘The family court can be very good and very awful,’ he says.

‘On the one hand, the judges work extremely hard to come to a difficult decision. On the other hand the court can sanction to a local authority the taking of children into care based on flimsy evidence, or rely solely on expert evidence that has not been subject to proper public scrutiny.’

Does he plan to write any more books about the law?

‘I could spend the rest of my life writing books set in the law,’ he says, ‘because there is so much human drama and there are so many ethical dilemmas. As well as stupidity and brilliance.’

The Children Act is published on 2 September in hardback.