LONDON (Reuters) - A strike by train drivers which has brought rail services in southern England to a standstill and caused chaos for hundreds of thousands of London commuters will continue after talks on Thursday failed to end the dispute.

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Drivers on the Southern Rail network will begin a 24-hour stoppage at midnight following two days of strikes earlier in the week which caused Britain’s worst rail disruption for two decades.

“Passengers and businesses are being held to ransom by the unions’ wholly unjustified and unnecessary industrial action,” said Nick Brown, Chief Operating Officer of Govia Thameslink Railway (GTR).

The dispute between the drivers’ union ASLEF and Southern, run by GTR, a joint venture owned by London-listed Go-Ahead and France’s Keolis, centers on whose role it should be to open and close the train doors.

The union says it should be the job of a conductor, a second onboard staff member, as a safety issue while the company says driver-only operated trains already run across the rail network without any problems.

Southern said talks at the conciliation service Acas had failed because the union would not shift its position of opposition to the company’s modernisation plans.

“ASLEF claims drivers closing doors is inherently unsafe,” Brown said. “For 30 years trains have been running up and down the country’s railways this way and today over a third of the national train network runs this way.”

Commentators said this week’s strikes would have the biggest impact since action by signal workers in the mid-1990s and Prime Minister Theresa May has called the strike “appalling”..

Her spokesman said on Thursday: “It is disappointing to see that the talks have ended today without any resolution but we would urge all parties to get around the negotiating table again and come up with a solution to end this.”

A series of strikes on Southern this year has caused misery for commuters, some of whom say they have even lost their jobs because they could not get to work.

However, many blame the company for the problems and say the government has done nothing to resolve the dispute.

Southern’s parent company Go-Ahead said on Thursday its full-year expectations for its rail division were slightly below previous forecasts due to the repeated strike action on its Southern rail contract.