UPDATED 08.35

THE longest strike yet in the driver-only operation dispute on Southern has begun, and RMT conductors are set to maintain their walkout until midnight on Friday.

Tempers are shortening on all sides. Southern said it was 'deeply disappointed and angry on behalf of our passengers', but the RMT accused the Department of Transport of acting behind the scenes to sabotage the talks, while Labour said the failure of negotiations was a 'missed opportunity'.

Southern said there are no trains at all on some routes, while services will cease by 18.00 on others.

The walkout follows a breakdown of talks at ACAS on Friday. The RMT had offered to suspend this week's strike if Southern's owner Govia Thameslink Railway accepted a proposal which is currently on the table in a similar dispute with ScotRail, where industrial action has been suspended.

Under this deal, conductors would maintain their titles and most of their safety-critical responsibilities, so that a train could not run without a conductor on board. Responsibility for operating the doors on ScotRail trains is still an outstanding issue.

Southern responded with a new 'eight point plan' which included fresh concessions, such as collective bargaining rights for the new on-board supervisors, a joint review of the jobs of the supervisors after 12 months of operation and a guaranteed minimum level of voluntary overtime. However, the company has stopped short of guaranteeing that trains would never run with only a driver on board.

Govia Thameslink passenger service director Angie Doll said: “RMT’s plan to cease the dispute should GTR agree to the terms agreed in Scotland recently is a complete red herring. This amounts to a continuation of the current operating model and delivers none of the punctuality and customer service benefits we are determined to deliver to our passengers.”

She also expressed Southern's anger that the negotiations had failed, saying: "We have gone the extra mile with our compromise offer, but the RMT has made it clear they are not prepared to negotiate. They did not want to discuss the role of the on-board supervisor and remain rigidly opposed to evolving the role of on- board staff to focus more on customers.

“We plan to have just as many services staffed with on-board supervisors as we do with conductors today. We simply want the flexibility to be able to run a train without a second member of staff on board, if they are unavailable so we can get our passengers on their way. To provide assurances that we would do this only when absolutely necessary, we said we’d agree with the RMT a list of binding rules to dictate when this could happen – such as during severe disruption. Their refusal to even discuss this demonstrates their complete unwillingness to compromise."

However, the RMT has alleged that the Department of Transport had set out to sabotage the negotiations.

The union's general secretary Mick Cash said: “It was clear right from the start of these talks that there was no serious intent from Govia Thameslink to engage in genuine negotiations and that their script was being written from behind the scenes by their government paymasters. You would have thought they would have taken our arm off when we offered to suspend the action in return for a series of guarantees that simply mirror the proposals from ScotRail just a couple of a few days ago.

“I have been involved in countless negotiations and have never witnessed a farce like this."

Labour’s shadow transport secretary Andy McDonald said: “This is a missed opportunity. GTR had the chance to demonstrate a basic commitment to passengers and to improve industrial relations but have instead opted to reject the compromise on offer.

“If, as has been suggested, DfT officials are found to be dictating GTR’s approach to this dispute by introducing unreasonable qualifications and demands at a crucial stage in the negotiations, passengers will be rightly incensed that the Government is intervening in such an unhelpful manner.

“Every day that passes without a settlement, the impression grows that the Government are more interested in picking a fight with trade unions than sorting out the abysmal services on Southern."

Routes with no services include the Uckfield line beyond Oxted, between Clapham Junction and Milton Keynes Central and between Lewes and Seaford. There are also no trains between Preston Park and Hove, or Dorking and Horsham, while Southern will not operate between Chichester, Portsmouth and Southampton. The Southern website has the full list, and also shows restrictions affecting services on other lines.