Train drivers have rejected a deal thrashed out between union bosses and Southern Railway - sparking fears of further strikes as the long-running row over driver-only trains now looks set to rumble on.
Passengers have been hit by long delays and cancellations as a series of strikes were held amid the dispute with Southern.
The row has been ongoing for almost a year, centred on staffing issues - including whether a second, 'safety-critical' member of staff should be guaranteed on trains.
Drivers' union Aslef agreed the deal after 11 days of talks with the company earlier this month - but members voted it down by 54.1 per cent in a turnout of 72 per cent.
Speaking after the results of the ballot were announced, general secretary Mick Whelan said:
We understand and support the decision arrived at democratically by our members and will now work to deliver a resolution in line with their expectations.
The union said of the 953 ballot papers sent out, 693 were returned. There were 317 votes in favour (45.9 per cent) of the proposed deal, and 374 against (54.1 per cent), with two invalid papers.
The agreement also drew the criticism of sister union the RMT (Rail, Maritime and Transport Union), which described it as a "shocking betrayal" of workers and passengers.
Aslef bosses argued that the deal had been "misunderstood", and insisted it would lead to safety improvements.
Nick Brown, chief operating officer at Govia Thameslink Railway, which runs Southern, said:
Naturally we're saddened and hugely disappointed, as will be our passengers, with today's decision by drivers, particularly as the agreement carried the full support and recommendation of the Aslef leadership.
Paul Plummer, chief executive of the Rail Delivery Group, which represents train operators and Network Rail, added: "This is a disappointing outcome that will worry hundreds of thousands of passengers.
"At the heart of this dispute are changes that will provide passengers with the better service they need and want.
"Where safety, jobs and pay are unaffected, the railway must be able to harness new technology and smarter ways of working to deliver the modern rail service the country needs."