Choo choo! All aboard for the 80th anniversary of Thomas the Tank Engine. The little blue steam engine and his colourful friends on the Island of Sodor are celebrating the milestone birthday with the release of the very first unseen pilot episode and a worldwide online auction of set props and memorabilia to raise funds for the National Autistic Society, more of which later.

Generations of young children have grown up with Thomas. The original 26 stories by the Reverend Wilbert Awdry have spawned a whole industry, including the TV series, toys, merchandise and even a theme park at Drayton Manor in Staffordshire.The Reverend originally wrote the tales for his son Christopher, inspired by a little wooden toy engine. After Awdry’s wife encouraged him to publish the stories, he selected a real locomotive for illustrator Reginald Payne to base the pictures on to create authenticity.

In 1979, writer and producer Britt Allcroft came across them and arranged a deal to make the television series Thomas the Tank Engine & Friends (later rebranded as Thomas & Friends). The programme became an award-winning hit around the world and is just as loved by young children today.

Rev Awdry’s granddaughter Claire Chambers has her own vivid memories, too.

“As a child, I loved going to his house in Stroud in Gloucestershire to stay and I remember grandpa reading us his Thomas stories at bedtime,” she tells the Daily Express.

“This was before the TV show and the toys so the books with their lovely pictures were all we had, but they were magical. My personal favourite was Trevor the traction engine who lived in the apple orchard because he used to give children rides. Everyone has a favourite engine. I remember family holidays would inevitably involve visiting a steam railway, often Snowdon, and I have done the same with my own boys.”

Claire, 49, says her sons Henry, 13 (not named after the engine she insists!), and Gus, 10, also adored Thomas growing up and like many mums, she is keeping all the wooden brio toys for the grandchildren.

“I remember Henry always holding a little wooden engine in his hand. He wouldn’t put it down. We used to take the boys to those ‘Meet Thomas’ days out at steam railway centres and I used to love seeing the faces of all the young children, the joy and excitement on their faces at meeting Thomas.

“When my grandfather wrote these stories he had no idea what a huge global phenomenon it would become. I remember a box of merchandise arriving at his house and him being very non-plussed by the plastic coat-hangers with pictures of his engines on.”

Claire believes the fact her grandfather based the stories on real locomotive events added to their appeal.

“He was always very careful to make sure he followed the railway rules and what happened in the stories came from real incidents that he had heard about or read about in railway magazines. As a family, we are very proud of him and are happy that these timeless stories continue to entertain children and hopefully in another 80 years time, they still will be.”

Ian McCue, who served as a producer on Thomas for several series, says: “Thomas is still as popular and relevant as ever. He has of course been updated over the years and the series has evolved, but at its heart, it is still about trains and railways. You still see little children on train platforms today during school holidays all excited shouting, ‘The train is coming!’

“New characters come along and we have adapted to the modern world but it is still all about that golden age of the railway that young children love – and often that love stays with them into adulthood.”

The adaptations Ian is referring to were in answer to criticisms the early shows lacked any strong female engines. Annie and Clarabel were merely Thomas’s coaches and then there was Daisy, a diesel railcar – highly-strung, lazy, and with long fluttering eyelashes.

“We needed to address the gender imbalance so we introduced Emily who stood alone with the boys as a strong female role model,” admits Ian. “We also introduced the first black engine, Nia, from Africa. We consulted with the United Nations on this.” Other new characters included Ashima from India, Yong Bao from China and Shane from Australia.

“Some of the old engines were replaced by new characters and this too attracted criticism,” continues Ian. “But whatever the changes, the values and lessons Thomas tries to instill in a younger audience remain the same – patience and the importance of good communication. From the ages of two to four it entertains and educates in its gentle way.”

Claire agrees and says she hopes the introduction of more female characters continues to attract young girls to the stories as well.Thomas has always been especially loved by young children on the autism spectrum. “My grandfather never wrote the stories with autistic children in mind, although he did base some of the characters on children he knew, but I am pleased children with autism love it so much,” she says. “I think the expressions on the engine’s faces are very easy to read, which of course helps.”

Ian adds: “There is a huge community around Thomas and that includes many people on the spectrum. I think what also appeals to them also are the routines and order of the railway. It runs to a schedule. The bright colours of the engines and calmness of the shows – compared to a lot of other children’s TV and cartoons – make it an excellent watch for them.”

Like many parents, Ian remembers getting up at 5.30am to watch Thomas with his two-year-old. “As a storyteller, I love the morals of the stories. They are all about doing the right thing, the friendships, the teamwork,” he says. “Getting up at that time with your kids, you want a nice gentle start to the day and it is.There is a romance about steam engines that lasts into adulthood, long after people have grown out of Thomas.”

Ian is excited about the release of the original pilot, which has been cleaned up, fully digitised and set to a bespoke music score by the original composer Mike O’Donnell. It also includes unheard voiceover from Beatle Ringo Starr, who narrated the show – and Ian promises “diehard fans will love it”.

But the pilot wasn’t without its hiccoughs in those early days. “The original had way too much steam. Smoke pellets were put in the funnels but when they were released you couldn’t see a thing. And they had to replace the plastic engines with brass ones, I think. For some reason the plastic stopped the signal from the remote control.”

As for the Prop Store auction, which goes live on the 80th anniversary on Monday and runs until May 28, Ian calls it a chance for fans to own a piece of the show. Mattel UK will pay all proceeds to The National Autistic Society, the UK’s leading charity that provides support, guidance and advice for autistic people and their families.

Ian says: “When the show went CGI in 2009, much of the set and props that didn’t go to Thomas Land went into storage. I like the idea of props that have been stored away in the dark for years suddenly having a new lease of life on someone’s bedroom shelf where they are loved and dusted instead of sitting hidden somewhere.”

The 200 lots include original pieces from the brand’s history and items signed by celebrities who have voiced Thomas & Friends characters over the years, including actors Olivia Colman, Eddie Redmayne and Hugh Bonneville. There is also original artwork from the iconic stop motion series and props such as vehicles, figurines, animals and buildings, up for grabs.

Claire says: “I have all the books signed by my grandfather but I might have a look see if there is anything I fancy! I remember being taken to the TV studio when I was about 10 and there was this huge model railway. I accidentally stepped on a pedal and set all the steam off.”

No doubt that caused some “confusion and delay” as Sir Topham Hatt – who we no longer refer to as the Fat Controller of course – would say.

* Watch the original and newly digitised pilot episode, Down the Mine, on YouTube/@thomasandfriends from 6pm tonight. To register for the live Thomas & Friends Online Auction, visit https://propstoreauction.com/auctions/info/id/442