Leading politicians in northern England have demanded a cut in fares on routes that still use the much-derided Pacer trains.

In a letter to Northern Rail, they say passengers deserve financial compensation for having to use the “buses-on-rails” that were due to be retired by the end of the year.

The Manchester mayor, Andy Burnham, the Sheffield city region mayor, Dan Jarvis, and the Leeds city council leader, Judith Blake, told the train operator that the continued use of the old carriages was “unacceptable” and that an urgent commitment to reduced fares “is the very least that could be done”.

The diesel-powered Pacers, built as a temporary stopgap in the 1980s from bus frames set on train wheels, do not comply with disability regulations that come into effect in the new year and still have toilets that flush on to the track. It emerged over the summer that, because of a delay in manufacturing their replacements, they would not be scrapped by 2020 as promised by the rail franchise.

The city leaders express “deep disappointment and frustration” in the letter, which was sent to David Brown, the managing director of Arriva Rail North, which owns Northern rail. They also ask for “urgent assurances” regarding the arrangements planned for customers with accessibility requirements while the Pacers remained in use.

Northern's Pacer trains to run into 2020 despite retirement pledge Read more

They say the “widening disparity between transport investment” in northern England, compared with the south has been underlined by the continued use of Pacers, but also acknowledge that withdrawing them before the replacements were ready would be a worse solution. The “retention, for a short, time limited period appears to be the best of an extremely poor range of options”, they write.

Blake said the withdrawal of Pacers was “one of the centrepiece commitments made in the Northern franchise”, adding: “The fact they will still be running in 2020 is symbolic of the broader issues with this franchise which continues to deliver an unacceptable level of service to passengers.”

The three politicians have requested a meeting to iron out a compensation package and promises regarding accessibility over the next week.

Last week, the transport secretary signalled that the Northern rail network could be renationalised after years of late and cancelled trains. Grant Shapps said he had asked the company, which runs routes from Newcastle to Leeds, Liverpool, Hull, Manchester and Stoke, to draw up proposals to improve the service, saying it could not “continue delivering in the current delivery method”. He also said he was “hugely impatient [to see] the extinction of Pacer trains”.

A spokesperson for Northern said “a small number of Pacers units” would need to be used “for a short period of time in 2020”. It said the first Pacer went into retirement in August, and “the majority of Pacers” were expected to be removed by the end of the year.

The company, acknowledging that “customers will be disappointed”, said it was “finalising proposals for customer support and offers” for passengers who travel on Pacers in 2020.

It added: “From today, Monday 21 October, we will have 29 of our 101 new trains in service for customers and a further 27 new trains are in final testing or being used for driver training.

“We agree the north deserves the best possible rail service and are working hard to improve performance and reliability for customers.”