Train enthusiasts poured into Dereham station for a classic loco's anniversary cavalcade – which also signalled the completion of a long-awaited railway improvement.

More than 2,500 people were estimated to have used the Mid Norfolk Railway (MNR) at the weekend to celebrate the golden jubilee of the English Electric Type 3 diesel locomotive – known as the Class 37 – which first operated in 1960.

A 12-strong collection of Class 37s, showing the evolution of the engine from the 1960s onwards, was used on the line.

Hourly departures from Dereham and Wymondham were packed with travellers eager to be pulled along by one of the most popular and versatile workhorses of the UK's rail networks.

And, halfway along the route, they became among the first to use the �50,000 Thuxton passing loop, which was formally opened on Friday. The new passing point, built by a volunteer workforce and paid for by the railway's own fundraising, will enable the MNR to double its capacity by running two trains on the line simultaneously for the first time.

It will help generate the extra revenue which could speed the railway's goal of expanding the line northwards towards North Elmham within the next two years.

James Steward, the MNR's operations director, said: 'It was a huge undertaking, and I am absolutely thrilled to see it completed.

'We have been constantly growing for the last five years, but we couldn't sustain it while running just one train at a time.

'More than 100 volunteers have worked on the passing loop in some shape or form, and it would not have happened without them.'

Among the spectators was Glen Withers, 51, from Dereham, who said: 'When I was kid these were the nasty machines which were taking over from steam engines, but now they have earned their place in history.'

Mr Steward said he had been 'blown away' by the success of the event.

'All the B&Bs have been full, and so the great thing is that the railway is contributing to the local economy,' he said.