Frances O’Grady, who has been personally involved in two weeks of intensive talks about whether drivers, represented by the Aslef union, or guards, represented by the RMT union, should close train doors, said: “We are pleased to announce that Aslef and GTR Southern have reached an agreement. For the avoidance of any doubt, this means that subject to a referendum of Aslef members on Southern, the dispute between Aslef and Southern is over.”

Members of Aslef have been staging an overtime ban, with several bouts of all-out strikes that brought the network to a standstill.

Aslef’s general secretary, Mick Whelan, said the agreement with the train operator, GTR Southern, has “the full recommendation” of both the negotiating team and the union’s executive committee.

Details of the deal have not been revealed, but it is believed that the drivers have agreed the basic principle of extending “Driver Only Operation” (DOO) across the network.

Aslef members are expecting to endorse the agreement in a vote early next week. But the biggest dispute on the railways since privatisation two decades ago is far from over.

The RMT union, which represents train guards, was not involved in the talks between Southern and Aslef. After the TUC announcement, the RMT’s general secretary, Mick Cash, described the process as “appalling”, saying:

“We have no details whatsoever on any deal that has been agreed by the parties who were granted a seat at the table.

“Consequently, we have no information on what impact any deal that may have been reached will have on nearly 500 guards who have been involved in an industrial dispute over safety for the best part of a year.

“That is an appalling way for that group of workers to be treated.”

Nick Brown, chief operating officer of Southern, said: “We’re open to talks with the RMT at any time.”

Mr Cash responded by saying: “Once we have the full details of the deal that has been struck today, and an assurance that the terms of reference of those talks will focus on the retention of a second safety-critical member of staff on Southern services, we can agree an immediate date for negotiations to commence.”

The tone of the RMT’s response indicates that the union will continue to demand that the guard must operate the doors. But the Department for Transport is insisting on modernisation. So Southern commuters can expect more the current tally of 29 days of strike action to increase.

At the heart of the dispute is a brief statement contained in the 2011 McNulty Report on value for money on the railways:

“Driver Only Operation is a safe method of operation and improves performance, with fewer human interactions involved in the door opening, door closing and dispatch procedure.”

The RMT fears its members will see their role diminished and jobs will go, It won a partial victory in Scotland, with drivers opening doors and guards closing them.

Mr Cash announced a new battlefield over the issue, with guards on Merseyrail being balloted for industrial action.

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Meanwhile, Southern commuters will note the combative tone of the RMT leader’s assertion: “We will not agree to any extensions of DOO and will fight to retain the safety critical role of the guard and to keep a guard on the train.”