Southern Railway workers are said to be "standing firm" on the second day of strike action in the bitter dispute over the role of conductors.

Members of the Rail, Maritime and Transport union have walked out for three days, forcing the cancellation of hundreds of trains.

The union is planning further strikes in the coming weeks as the long-running row remains deadlocked.

Members of the train drivers' union Aslef on Southern are to be balloted for strikes over driver-only trains. Voting will be held next month, raising the possibility of joint strikes in December.

Mick Cash, leader of the RMT said: "RMT Southern guards are standing firm again this morning as they fight to defend safety and access on Britain's biggest rail franchise.

"RMT thanks the travelling public for their support and understanding as our members demand that passenger safety be put before private profit.

"Southern Rail need to get out of their bunker and start serious and genuine talks with the trade unions."

TUC general secretary Frances O'Grady said Southern should stop blaming unions for "its own failures".

She added: "Southern should not be gambling with passenger safety. Having a properly trained guard on board is the very least commuters deserve.

"Passengers will be at a loss to understand how a company that has been cancelling so many rail services can generate such massive profits and not be held to account by the Government.

"The travelling public deserve a much better deal."

Charles Horton, chief executive of Govia Thameslink Railway, which owns Southern, said in response to the TUC: "This is simply scaremongering.

"We'll have a second person rostered to work on every train that has one now - in fact they'll be on more trains. They will still be trained to assist elderly and disabled passengers, provide direction in emergencies and keep order.

"They will not be involved in the dispatch of the train because on modern trains the driver can do this - it's how a third of the UK's trains have operated for over 20 years.

"The changes we are making will provide passengers with better on-board customer service and fewer delayed trains."

A spokesman for the Rail Delivery Group, which represents train operators and Network Rail, said: "The TUC's inference that Southern is generating 'massive profits' is not correct. It is public knowledge that Southern has been supported financially by its owners, including Go-Ahead which is a British-based transport company operating successfully in many countries around the world.

"It is important that debates about the railway's future are based on open, honest discussion of the facts."