Members of the Aslef union have rejected a deal aimed at ending a long-running dispute with Southern Railway, the company said.
Members of the union had voted on a deal to help resolve the bitter row over staffing and driver-only trains.
Passengers have suffered almost a year of disruption on some of the busiest routes in the country because of industrial action and other issues such as staff shortages.
Aslef leaders had recommended that the deal should be accepted, believing it is the best that can be achieved.
A previous proposed agreement was surprisingly rejected by drivers and today’s result was expected to be close.
Union leaders - who held almost three weeks of talks with Southern following the rejection - argued the deal means Southern will have a second, safety-critical person on trains except in exceptional circumstances such as staff affected by last-minute sickness or travel delays.
Andy Bindon of Govia Thameslink Railway, Southern’s parent company, said: ‘It’s a hugely disappointing outcome for our passengers, particularly as the agreement carried the full support and recommendation of the Aslef leadership.
‘We have shown a willingness and desire to find a solution to their dispute and we will now, once again, sit down with the union, understand the issues which led to this regrettable decision by the drivers and try and find a way forward to resolving it.’