Wanted: actor to star in a new film franchise. Requirements: short legs, fat belly and the potential to throw a small girl into the nearest hedge.

Sixty years after they first appeared in Punch magazine, the comical ponies created by Norman Thelwell are moving to the big screen.

The Thelwell family has agreed a deal to turn the late cartoonist’s beloved creations into a live action feature film, in what it hopes will be the beginning of a franchise to delight a new generation.

Norman Thelwell produced more than two dozen books, beginning with Angels on Horseback in 1957.

Credit: Getty

The search is now on for a girl to play Penelope, the eager young rider, and a pony to play Merrylegs, her recalcitrant steed.

The film, to be called Merrylegs: The Movie, will be set in Snowdonia, Wales, and shooting begins later this year.

Penny was named after Thelwell’s daughter, Penelope. Speaking to The Telegraph, she said her father deserves to be a household name once more.

"There are lots of fans who say, ‘My grandmother gave the book to my mum, they’re somewhere in the attic.’ And there are a whole lot of people who love to follow his work, and they know the ponies, but they don’t know the name ‘Thelwell’.

"They know the drawings but the name has become a little bit of a thing of the past, so this is a wonderful way of bringing it back to a new generation while also being very nostalgic for the people who grew up with it."

Thelwell sent his first cartoon to Punch magazine in 1953, based on the ponies he would see being ridden past his home in the West Midlands. He went on to produce more than two dozen books, beginning with Angels on Horseback in 1957.

All were best-sellers, but Penny said that the books are no longer so easy to find.

"I haven’t seen any of them in WHSmith for years. That used to be the big thing for Dad, when the new books were published and they were so popular, so it would be lovely to bring back that recognition," she said.

The Telegraph’s obituary of the author and illustrator in 2004 noted: “Thelwell’s books had a place in the downstairs lavatory of almost every country house. Ponies of a certain shape and temper became known as ‘Thelwells’.”

Candida Bray, the director, said she was currently working with ponies and their trainers in order to understand what the animals can be trained to do, and what will be added later through special effects.

"I’ve been amazed to see what people can get their ponies to do. We’ve just been filming a pony happily sitting on a beanbag," she said.

Shetland ponies and Welsh mountain ponies are currently her favoured breeds, and anyone who believes they have a pony that would make the perfect Merrylegs should contact the production company, Blenheim Films.

"Casting the right pony is very important. We’re looking for very expressive ones," said Bray. "Thelwell ponies are laden with character. It’s a sparkle, a cheeky sparkle that we’d be going for. And also a big fat tummy, slightly foreshortened legs and slightly unkempt hair."

Thelwell's drawings were exhibited in Germany in 2017, the first time they had been shown outside the UK

Credit: Ingo Wagner/DPA

Thelwell loved drawing horses but famously never rode one. His daughter said: "He liked to know what was going to happen, and with a horse you never know. But he absolutely loved drawing them. In his work, the animals are always the wise ones."

Thelwell’s other passion was for the environment. His 1971 book, The Effluent Society, was ahead of its time in its call for preservation of the natural world.

Bray’s previous films include Trashed, a documentary about the environment, and she said Merrylegs: The Movie would acknowledge the theme.

She added: "I love the countryside and hopefully seeing that on film will get a new generation to fall in love with getting outside instead of being stuck in front of screens."

The film is set for release in 2023, marking the centenary of Thelwell’s birth. A television series based on his autobiographies is also in development.