Rail workers are threatening court action over what they say is a deliberate ploy by bosses to refuse them holiday time.

Arriva Trains Northern is involved in what has now become the rail industry's longest-running industrial dispute since 1922, with conductors striking over pay.

As hundreds of train conductors stage their fourth 24-hour walk-out over the festive period today, union leaders accused management of withholding leave time in a ploy to break workers' resolve.

Stan Herschell, regional organiser of the RMT union, said: "My members are owed something like 2,000 holiday days. Arriva's leave time runs from January to December, so there is no way workers can take it.

"Management have simply refused to let people have time off. Apparently, this isn't covered under employment law, so we are going to go to County Court to see what we can do about it."

He accused Arriva of "bullying tactics" claiming members had been intimidated and threatened during the dispute, which will be a year old on January 24.

Talks with mediators ACAS broke down earlier this year, and there looks to be no end to the dispute. "We believe our argument was fair and just when we started in January 2002 and it is still fair and just nearly a year on," said Mr Herschell.

"There is a lot of determination among the conductors in this union and they are very solid.

"We are a democratic union and the members will tell me when they've had enough and that's certainly not the case now."

The union leadership is set to meet early in the New Year to take stock and decide on the next stage of the action. Mr Herschell hinted that members could be balloted again to see if they want to carry on with the strikes.

A spokeswoman for Arriva Trains Northern, which provides regional train services across the north of England, said yesterday that more than a quarter of conductors were expected to work and 80 per cent of the firm's normal network was expected to be running.

She declined to comment on the issue of holiday time owed to workers.