Judith Kerr, one of the UK’s most beloved authors and illustrators, has revealed that the only exam she ever failed was for book illustration.

Speaking at the Hay literary festival in Wales, the 94-year-old author of classics including The Tiger Who Came to Tea and the Mog series said she failed illustration while enrolled at a London art school after the end of the second world war.

Kerr, whose Jewish family fled to the UK from Germany in 1933, said that, as a migrant, she was only eligible for a trade scholarship. She longed to study life drawing, so was encouraged by a tutor to pretend she was studying illustration, a trade, while attending life drawing classes.

“Unfortunately, in my last term, some bureaucratic person decided we must all get a diploma at the end of our time at art school, which had never existed before. We had to have an exhibition of our work and write a thesis. Of course, I hadn’t done any illustration. So I tried desperately to do some, but I couldn’t, of course,” she told the crowd.

“To justify [the fact that] I hadn’t done any illustration, I wrote a thesis saying that illustration wasn’t really a separate branch of anything. ‘Look at Picasso,’ I said, who had just done wonderful illustrations for Buffon’s Natural History. It didn’t go down at all well. So I failed. It’s the only thing in my life that I’ve failed. I’ve been horribly good at exams but the only exam I’ve ever failed is book illustration.”

Kerr, who only started drawing and writing books in her 40s, also revealed that she would no longer be writing books about her current cat Katinka – who, like her previous cat Mog, has starred in a few of her picture books. She said that her next book would be out in October, but she could not yet reveal further details.

Recalling the moment, aged 17, when she confronted her mortality during the 1940 Blitz, she said: “It looked absolutely, certainly very alarming.[I thought:] ‘Oh dear, what a pity. I’ll never get any older, I’ll never know or find out what I can do.’ And then, the invasion didn’t happen.

“I thought, like many other people in this country, that Hitler would win and the world would be taken over, more or less. And that didn’t happen. And then, many years later, in the cold war, it looked as though the world might become communist. But that didn’t happen either. Well, with luck, it’ll be alright.”