Drivers working for Southern Rail, which runs trains from central London to Gatwick and Brighton on the south coast, will walk out for 48 hours tomorrow over a long-running dispute about whose job it should be to open and close the train doors.

Southern, run by Govia Thameslink Railway (GTR), a joint venture owned by London-listed Go-Ahead and France's Keolis and Britain's largest train operator, said there would be no services tomorrow and Wednesday as a result of the action.

It gave passengers a simple message: "Please don't travel".

"In essence this is a battle between the unions and the management over whether they will allow new technologies and new ways of working on the railway," Transport Secretary Chris Grayling said in a letter to Southern passengers.

"It is deeply, deeply unfair on the passengers who are left in the middle of this dispute."

Southern users have already endured months of cancellations and delays because of high levels of staff sickness which were followed by strikes by conductors, staff who currently have responsibility for the carriage doors.

Unions argue Southern wants to extend the use of driver-only operated trains and so reduce the safety role the conductors play. Southern says its changes would not cost any jobs but would lead to fewer train cancellations as services would no longer require both drivers and conductors.

The operator, which handles 620,000 passenger journeys every day, failed in a bid at London's High Court last week to get an injunction to stop the strike and made a last ditch bid at the Court of Appeal to overturn that decision.

"Even if we are able to stop the strikes through the court, services will still be very heavily impacted tomorrow," said Angie Doll, Southern's Passenger Services Director.

"We will work through the night to try and provide as many services as possible, but we are still advising passengers not to travel as we will not be able to offer a robust service they can rely on."

Another strike by drivers and conductors is due on Friday, with more walkouts planned by conductors this month and a five-day stoppage by both from Jan. 9.