Crucial talks aimed at averting a week-long strike on Southern Railway will start on Wednesday amid fresh warnings of disruption if a deadlocked row over the role of conductors is not resolved.

Members of the Rail, Maritime and Transport union are due to walk out for five days from next Monday in protest at changes set to come into force on August 21.

Southern, part of the giant Govia Thameslink Railway (GTR) franchise, has published details of the service it plans to run if the strike goes ahead.

On the Brighton mainline, trains will run but are expected to be very busy as a reduced timetable will be in place.

This will see significantly reduced services between Brighton, Lewes and Eastbourne; Brighton, Worthing, Littlehampton and Bognor.

There will be no services between Polegate, Hastings and Ashford International. The line between Chichester and Havent will also not be in use for Southern services.

No trains will run to London via Lewes and Wivelsfield.

Complete line closures will be in place from Uckfield and Hurst Green.

A replacement bus service will continue to run between Seaford and Lewes.

The company warned that the union had to call off the action by Thursday afternoon to avoid the strike timetable.

Two days of talks are planned at the conciliation service Acas.

Southern said that by using "contingency conductors" it expects to run almost 60% of its normal timetable, or two thirds of a temporary, revised timetable it brought in last month to deal with staff shortages.

A statement said: "There will be a restricted service, with many routes having fewer trains, and, unfortunately, on some routes there will be no service at all. Trains on many routes will start late and finish early."

GTR passenger service director Angie Doll said: "We are sorry that our passengers once again look set to suffer further disruption because of the RMT. The union must call this action off by Thursday afternoon if we are to avoid having to put in Monday's strike timetable.

"This action is not necessary. Our new on-board supervisors will no longer close the doors, a task that passes to the driver with the aid of CCTV. This will cost no-one their jobs, and frees up staff on board trains to better serve passengers.

"As many services will have staff on board as they do today and our on-board staff will have an improved role which better meets the needs of passengers, securing their valued position on the railway for the long-term.

"And there will be fewer train cancellations in future. Currently, conductors are tied to specific routes and services, but the new on-board supervisor will be able to go anywhere on our network, significantly reducing the perennial problem of train cancellations due to conductors not being available when they're delayed by disruption, for example."

Southern said the revised timetable, which has 341 fewer trains, will resume after the strike ends, for a minimum three weeks.

Mick Cash, general secretary of the RMT, said: "RMT enters these talks in good faith. It must be the priority of everyone on our railways to protect and enhance the safety of the travelling public at this time of extraordinary pressure on our services. That is the fundamental issue at the heart of this dispute.

"RMT once again thanks the travelling public for their support for the front line rail staff whose job is to keep people safe on our dangerously overcrowded trains and platforms."