When my children were very little I started telling them stories. From the house in France where we spend our holidays you can see a castle, so we'd go for walks in the woods and I'd tell them stories about the castle. Usually they were about them and their friends, and how they'd outwit the evil Duke who lived there.

One day, when we were visiting the castle, my son noticed that the stone around the gate was coloured pink, and asked why. Stone goes pink if it's burnt in a fire, so I told him how the castle had been burnt. A long time ago there had been a war between the English and the French. An English army had come to the castle, laid siege to it and burnt it down. I described how soldiers must have piled wood against the gate while the defenders shot arrows from the battlements; and how from our house, that night, people must have seen flames leaping high into the sky.

That was a true story, and after that I often told my children stories from history. When we sailed past Bloody Point, on the River Orwell in Suffolk, I told them how King Alfred attacked a Viking fleet and fought them until the river ran red with blood. When we visited the Chateau of Versailles, I told them about the French Revolution, and how a crowd of poor people burst into the King and Queen's bedroom and dragged them away to Paris.

All the time I was writing history books for grown-ups. I realised that what I wanted to write next was a book of stories for everybody – stories from the past, stories that explain the people we are and the world we live in. I realised that all the stories I'd been telling my children fitted together to make one big story. And that was the book I sat down to write: our story – The Story of Britain.