Mallard had just hauled six coaches and another car up Stoke Bank, south of Grantham on the East Coast Main Line, at 75mph.

As the train came down the other side, she touched 126mph, bettering a German 1936 mark of 125mph, to establish a world record for steam locomotives which has never been beaten.

These days Mallard is on display at the National Railway Museum in York, which is this week celebrating the world speed record by one of its most famous exhibits.

To bring the moment to life in the museum's Great Hall, actor Chris Ford, from Platform 4, the museum's in-house acting troupe, recreated the moment that driver Joseph Duddington and fireman Tommy Bray coaxed their train to 126mph.

It was a curtain-raiser to a grand reunion on Saturday and Sunday at the museum, when Mallard will take its place next to three other steam legends – a sight unheard of in modern times.

All four of the streamlined A4 locos remaining in Britain – Mallard, Bittern, Sir Nigel Gresley and Union of South Africa –will back together for the first time since their heyday to celebrate the legacy of rail engineer Sir Nigel Gresley.

The secretary of the Gresley Society, Chris Nettleton, said: "It is testament to Sir Herbert Nigel Gresley's brilliance that 70 years on Mallard's record is still unbroken.

"Gresley is one of the greatest engineers the world has ever known and it is only fitting that the museum is taking this opportunity to demonstrate the sheer genius of his work."

NRM Director Andrew Scott added: "Aside from Gresley's pioneering designs, it was the crews on board Mallard 70 years ago that made the breaking of the record possible."