A 120-year-old mystery about what was once regarded as the world’s oldest operational steam locomotive has been solved – it’s a fake.

Railway enthusiasts in the past were so convinced that the Hetton Lyon locomotive had been genuinely built in 1822 that in 1902 the County Durham engine was hailed as one of the great survivors from the earliest days of the railway.

In 1925, it was chosen to lead the cavalcade which commemorated the centenary of the Stockton & Darlington Railway.

But, even in 1902, there were murmurings about whether it was genuine, and over the course of the 20th Century, those murmurings have grown.

Now researchers at Locomotion, the Shildon railway museum, have proved beyond doubt its true provenance.

“The press release of 1902 was, to use Donald Trump’s expression, fake news,” said industrial archaeologist Dr Michael Bailey yesterday as he announced the results of his findings in a virtual news conference.

Instead, he has shown that the Hetton Lyon was built in 1849-50 at the colliery on the edge of Sunderland.

“It is a wonderful rarity and a great survivor – a mid 19th Century industrial locomotive in working condition,” said Jim Rees, an early railways expert who used to look after the Lyon when it was stationed at Beamish Museum. “It has come to be regarded as an embarrassment, but now is the time to put it centre stage.”

The eight-mile long pioneering Hetton Colliery railway of 1822 was one of George Stephenson’s earliest projects, with his engines pulling coal down to staithes on the River Wear. He put his experience to good use three years later when he created the 26-mile Stockton & Darlington Railway, which is regarded as the world’s first modern railway.

In 1902, the colliery company billed Lyon as “the world’s oldest working steam locomotive” and announced it was retiring from active service.

“This claim went viral,” said Dr Bailey. “So many people wanted to see the loco that it was decided to keep it in operation, and for ten years, visitors came from all over to see it.”

The engine then broke down and was put in storage. “Such was its fame as the oldest working loco that they didn’t have the heart to scrap it,” he said.

It was in storage for more than a decade until the LNER restored it at considerable expense at the Darlington North Road works so that it could head the 1925 cavalcade, which was watched by more than 100,000 people as the engines travelled from Stockton to Darlington.

“I don’t think anyone ever challenged that it wasn’t built in 1822,” said Dr Bailey. “The whole parade was based around this early Stephenson loco.”

However, something wasn’t quite right about it and the doubts grew about it until last April, Dr Bailey and researcher Peter Davidson were called in by the National Railway Museum (NRM).

“We spent five minutes standing by it, and we said ‘there’s no way this could have been built in 1822’,” said Dr Bailey. The plates that the boiler was made out of were too large to have been rolled in 1822, and the chassis was too massive.

Dr Bailey has now proven that the plates were made at the Consett ironworks, which opened in 1848, and the engine was built at Hetton to Stephenson’s reliable, but old, design. Because it functioned so satisfactorily, it was kept going until 1902 by which time its real provenance had been forgotten.

Dr Bailey said: “Although it would have been exciting to uncover links to early Stephenson engines, the benefit to us today is that this remarkable locomotive would undoubtedly have been scrapped were it not for the tall tales surrounding it.

“The result of the Hetton myth is that we have an early and unique example of an industrial steam locomotive which tells us a great deal about the construction of early engines and components. What is most surprising is that the myth endured for so long and that the durability of the outmoded designs enabled the engine to continue operating for such a long time.”

Although Lyon – named after the family which owned the Hetton Colliery - is no longer one of the oldest in the world it is still of great interest.

“It is an incredibly significant survivor in the history of railways in the North-East,” said Andrew McLean, the NRM’s head curator. “Lyon is going to be one of the great attractions at Locomotion. We have a new building going up in the next two to three years to display more of the collection. It is all about putting the right objects in the right place to tell the story of North-East railways and their important role in creating such an important international network.”

It is hoped that Locomotion at Shildon, currently shut due to the pandemic, will be re-opening in the near future.