Thousands of passengers across south west Hertfordshire and North London face travel chaos as another train strike begins, affecting more than a third of its services.

Southern Rail workers, that are members of the Rail, Maritime and Transport (RMT) union, will mount pickets lines today with disruptions expected to continue until Friday.

Southern Rail said around 61 per cent of its normal timetable will run, but many routes will have fewer trains and some will have no service at all.

The row started from a dispute over the change to the role of conductors who currently still open and close doors on-board the trains.

But despite advising workers to accept new contracts from Southern, RMT told workers to strike.

RMT general secretary Mick Cash said: "The union intends to continue with the planned action and is examining the details of the paperwork."

He urged RMT members to continue preparing for the strike and to organise picket lines and protests.

Speaking yesterday, a Southern spokesman said: "On Friday they told their conductor members to accept a deal, and then tomorrow they plan to strike against it.

"It is a situation which will leave our passengers baffled, and in that context we are presently considering all possible options to stop the strike.

"We have written to the RMT about the validity of the dispute in light of recent developments. We await their response and will consider all possible options to stop the strike and that includes a legal challenge."

Hours before the walkout, RMT received a legal challenge, however it failed to prevent the latest action.

The RMT said earlier that Charles Horton, chief executive of Govia Thameslink Railway, which owns Southern, has been closely involved in discussions at the Rail Safety and Standards Board (RSSB) over the role of conductors.

The union claimed it had a leaked briefing memo showing Mr Horton’s links to the board, which it claimed proved the RSSB was not independent.

Southern denied the claims and the RSSB said it did not recognise the document that the RMT was referring to.

It added that that sections released by the RMT were not from a briefing memo, but instead from a publicly available research report.

A spokesperson said: "Charles Horton is one of our non-executive directors but was not involved in the research project which has been quoted in the document published by the RMT."