Workers on South Western Railway (SWR) have voted overwhelmingly to continue with industrial action in the long running dispute over guards on trains, threatening more strikes.

Members of the Rail, Maritime and Transport union (RMT) backed the campaign of action by 86% – the fifth time they have been balloted over the row.

Mandates for industrial action have to be regularly renewed under employment legislation, which the union accused SWR of using to “string out” the dispute.

RMT General Secretary Mick Cash said: “RMT has been forced under the latest wave of Tory anti-union laws to ballot for a fifth time in the rail safety dispute on South Western Railway under the six-month rule and once again our members have stood united and solid and have renewed the mandate to carry on the fight to put public safety before private profit.

“It is a disgrace that South Western Railway have yet again opted to play for time over the past six months rather than nailing down a solution to this dispute that puts safety and the guard guarantee centre stage.

“That is the package we have successfully negotiated in both Wales and Scotland and on a number of English franchises. It defies belief that we are being denied the same positive outcome on the South Western Railway routes.”

The union’s executive will consider the vote and make a decision on any future action.

Dozens of strikes have been held against SWR over the past few years in what has become one of the longest ever industrial disputes.

SWR runs services to and from London Waterloo, the busiest railway station in the country.

A SWR spokesman said: “We are very disappointed with the result of this ballot as we have been very clear that no jobs are at risk and we have offered a guarantee of a guard on every train as part of a framework to resolve this dispute.

“In fact, our plans over the course of the franchise mean we will continue to recruit and employ more guards, not fewer.

“The ballot result shows that many thousands of customers and colleagues could now be subjected to further strike misery at the behest of less than half our total guards workforce.

“It’s time the RMT union was honest with their members about what it is exactly they want given the assurances that have been provided by the company. The constant threat of further disruptive strike action is not fair on anyone.”

The RMT said it will be meeting the company on Thursday in a bid to resolve the dispute.