Transport Secretary Mark Harper has been urged to fund new Elizabeth line trains to help save the UK’s largest rail assembly factory.

Alstom is consulting on potential redundancies believed to be around 550 at its train manufacturing site in Derby, while 780 contractors are also at risk.

This is due to a gap in its order book.

In a joint letter, bosses from Transport for London (TfL), Alstom and trade union Unite urged Mr Harper to agree to fund new trains for the Elizabeth line, which runs between Berkshire and Essex via central London.

They stressed the importance of a quick decision before Alstom demobilises its production facilities for the Aventra trains used on the route.

The letter warned that the Government’s decision for Old Oak Common – in the west London suburbs – to be the capital’s HS2 terminus for several years means more pressure will be put on Elizabeth line services at the station.

The letter stated: “The additional trains will enable TfL to operate a higher frequency of services to Old Oak Common to relieve wait times at the station, reduce crowding on trains and provide shorter journey times for more customers using Old Oak Common station.

“Relying on the existing services on the western route would undercut the benefits brought by introducing high speed rail travel between Birmingham and London; it would be detrimental to the local area, as it would fail to cater for the growing community around the station which has 26,000 homes and 56,000 new jobs in the pipeline; and the consequences would extend to the national economy.”

TfL believes the Government should pay for at least five additional trains at a total cost of around £120 million, because its HS2 policy will cause extra strain at Old Oak Common.

The letter added: “Given the small size of the order required, delaying it would require Alstom to mobilise a new production facility at a much higher cost.

“If we miss the opportunity with Alstom, it may be impossible to achieve elsewhere and HS2 will not achieve the programme aspirations for Old Oak Common.”

A Department for Transport spokesman said: “We have been engaging extensively with TfL and Alstom on this issue for months and are continuing to work with them.

“A dedicated cross-Government taskforce has also been set up to properly support workers during what will be a concerning time.

“The Transport Secretary will respond to the letter shortly.”