Twenty-one years after James Herriot last put his hand up the back end of a cow, the much-loved vet is returning to the small screen this Christmas in a spin-off of All Creatures Great and Small.

But viewers of BBC1's Young Herriot will see the Yorkshire Dales swapped for urban deprivation in 1930s Glasgow as the drama follows the young vet as he learns his trade at college alongside his close friends, feminist Whirly Tyson and aristocrat Rob McAloon.

In its heyday, All Creatures Great and Small, based on the diaries of real-life vet Alf Wight, who wrote under the pseudonym James Herriot, pulled in audiences of about 13 million. It was broadcast by the BBC between 1977 and 1990.

Young Herriot is part of a trend for telling the story of popular TV and film characters in their youth. ITV is making a prequel to Inspector Morse called Endeavour, while the BBC put the early years of Only Fools and Horses in the spotlight in Rock & Chips. And from the US there is a plan for a prequel to Sex and the City.

Young Herriot executive producer Cameron Roach said he thought the trend was due to the recession and nostalgia.

"We've discussed this and think that in these kinds of recessionary times, people want the reassurance of a product that they know," Roach said. "They want to go on a journey during a series but ultimately know it's going to be all right because it's about because it's about characters they know and love. Viewers also want to know what informed the characters and made them the person they are."

Roache added: "Of course everyone remembers All Creatures Great and Small with great affection but we wanted Young Herriot to be a different proposition for a 21st century audience. It's so rare to have three young leads in a period drama."

With other period dramas such as ITV1's Downton Abbey coming under fire over historical accuracy, the producers have sought to ensure that Young Herriot is packed with authentic details.

"We are under pressure for accuracy because of what's happened to other series," Roache admitted. "We are confident in terms of period detail as we were lucky to have access to the diaries that Alf Wight wrote at the time and have so much information about what the science and life was like in the 1930s – where people went hungry and there was no NHS."

Young Herriot co-writer Eileen Gallagher said they had felt under pressure to ensure the three-part drama lived up to the expectations of All Creatures Great and Small fans.

She added that the new series had the full support of the family of Wight. Christopher Timothy played Herriot in the original series, which also starred Robert Hardy, Peter Davison, Lynda Bellingham and Carol Drinkwater.

Young Herriot features rising star Iain de Caestecker, who plays the trainee vet with a Scottish accent. That may confuse some All Creatures Great and Small fans as Timothy's character did not have an accent, but Wight was raised on the edge of Glasgow.

Unusually for a BBC1 drama, it has three young leads, with de Caestecker joined by Ben Lloyd-Hughes, who plays McAloon and Outcasts actress Amy Manson, who plays Tyson.

Three episodes of Young Herriot have been filmed and, although the series begins in Glasgow, it goes on to feature the vet's exploits in the countryside.

Young Herriot was created by producer Kate Croft and the now-deceased All Creatures Great and Small screenwriter Johnny Byrne.

Croft said she was proud of the series, "but it is sad that Johnny is not here to see it".

Byrne, who wrote 29 episodes of All Creatures Great and Small, died in 2008.

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