How a wet Welsh summer helped create Winnie-the-Pooh

At the time, Brandreth said AA Milne was already a "successful" playwright, with 40 plays to his name.

But it was after the birth of his son that Milne turned his attention to writing for a younger audience.

During a rainy family holiday, Brandreth said Milne was "a bit fed up", adding he "didn't really like the other people he was with".

Confined indoors with little Christopher, Milne sat in a potting shed, feeling "gloomy" as the rain poured down, according to Brandreth.

There, he began writing children's verses - poems such as The King's Breakfast - which would eventually be compiled in his first book of children's poetry, When We Were Very Young, illustrated by EH Shepard, and published in 1924.

The 38th poem in that collection, Teddy Bear, marked the first appearance of Winnie-the-Pooh and his trusty ally Christopher Robin.

Released in America in 1925, the collection went on to become a bestseller.

"As it turns out," said Brandreth, "it's thanks to the rain in north Wales - on the so-called Welsh Riviera - that we have this lovely book, When We Were Very Young."

Subsequently, Milne began to focus on writing for children, with the first Winnie-the-Pooh story published on 24 December 1925.

By the 1960s, Disney had bought the rights for the character, later - in 2001 - paying approximately £239m to secure ownership until the copyright expires next year.

It was a deal which, Brandreth said, made the bear "hugely famous" worldwide.

Milne's books "were enormously popular right from the start," he said, calling him "one of the most successful children's authors of all time".

"The reason Winnie-the-Pooh has lasted a hundred years," he added, "is because it's so beautifully written".

"Those poems and stories work, no matter what age you are. They are full of fun.

"There's an enchanted world, full of cheeky and naughty things happening," he said.

"It's full of generosity, and what Milne called the 'pure happiness of childhood'."