Trains promised to National Railway Museum have not arrived because they are still needed on the beleaguered Northern line, it has been claimed.

The National Railway Museum in York said it had plans to display a Pacer model, which was built in the 1980s, as it was an important part of the UK's railway heritage.

However, the timing of the Pacer’s arrival as an exhibition has yet to be confirmed - as the carriages remain in use on Northern-operated railway routes.

The distinctive carriages are well-known across the north of England as they feature a bus body welded to a chassis. The models have been in service since the 1980s.

Northern offered its assurances that there were no plans to retain the trains beyond the end of 2019 - but Aslef, the train drivers’ union, said it showed passengers were being treated “little better than cattle”.

A spokesman for Northern responded: “We will start operating new trains worth £500 million during 2019 and are upgrading the rest of our existing trains that will be in use in 2020 and beyond.

"This upgrade does not include the Pacer trains because they will be leaving the Northern network."

It is understood trains are usually donated to the museum, who express an interest in certain models while they are still in service.