Their latest walk-out threatens to disrupt one of the world's most famous race days, but rail union members insist the safety of passengers would be put at risk if conductors were removed from trains.

Rail, Maritime and Transport members from Arriva Trains North - which operates Northern Rail - are set to join others from Southern and Merseyrail for the 24-hour strike on April 8, the day of the Aintree Grand National.

Talks between rail operators and the union have broken down after an agreement could not be reached on the future role of conductors - known as guards - on trains.

The row stems from plans to introduce driver-only trains by 2020. The RMT has questioned the safety of only having one member of staff on board at any one time.

Craig Johnston, RMT regional organiser based in Cumbria, explained that guards need to know more than 35 safety competencies, including evacuation procedures.

They are also trained on dealing with emergencies, fires and derailments and need to know about signalling and track layouts.

"All these skills will be lost if we lose train guards," he stressed. "We are not going to accept a situation where the railway is made much less safe and, in the long-term, much less passenger focused because of the Government and the train operators' insistence on driver-only operated trains across the whole of the north of England."

Commenting on the date of their latest strike, Mr Johnston said members were left with no choice.

"If you are going to take industrial action it's got to be on a day when people notice that you're going to take it, otherwise there's no point you being on strike," he said.

"We don't want to be engaged in industrial action at all. Our members lose money. Our members' job is to move people from A to B and keep the country running.

"Nobody wants to be in this situation but no one has been able to give us any alternative.

"[Rail bosses] have got time to avoid this strike by coming to a reasonable, sensible, settlement of the dispute. But if they don't, expect more of this."

Northern Rail runs trains all over the north of England including the west coast of Cumbria, and Carlisle to Settle and Newcastle lines.

In total almost 100 union members in Cumbria are due to take industrial action.

Richard Allan, deputy managing director of Arriva Rail North, said this week: "We are surprised that RMT has announced strike action for April 8 as we had been in contact with their officials to organise further talks.

"We have been clear that we want RMT, along with our people, our customers and stakeholders, to play a role in bringing our modernisation plans to life."

An Aintree spokesman, said was "unfortunate" an agreement couldn’t be reached at this stage.

"We hope this changes for our customers and staff and will continue to work with our transport partners to work out the best possible solution to ensure it has as little effect on our racegoers as possible," he said.

Jan Chaudhrey, managing director of Merseyrail has criticised the timing. He said the RMT had "sunk to a new low" by striking during British horse racing's top event.

He said: "Damaging the company and its passengers is one thing, but damaging the whole of the Liverpool city region on one of its proudest and most important days of the year is impossible to understand."