Workers on the South Western Railway will be balloted for strike action, RMT has announced, with the rail franchise branding the statement ‘unnecessary’ and ‘premature’.

The union has declared a formal dispute over the ‘failure to give clear, cast-iron assurances over the future of guards on their trains’.

Guards, commercial guards and driver members on South Western Railway and Island Line will be included in the ballot for strike action and action short of a strike.

Mick Cash, RMT General Secretary, said: “RMT has given repeated opportunities for First MTR to give us the assurances we have sought over the future role of the guards on their trains throughout the length of the new South Western franchise.

“They have refused to give us those guarantees and it is that failure which leaves RMT with no option but to declare a formal dispute with the company and to move towards a ballot for action.”

But the rail franchise claims a second person on the train will remain, and the number of drivers and guards will increase.

A South Western Railway spokesman said: “This dispute is unnecessary, we have made it perfectly clear that we plan to retain a second person on our services as we know that our passengers value the assurance and assistance a second member of on-board staff provides.

“During our franchise we will increase the numbers of drivers and guards so we can deliver more services for passengers. We look forward to talking with our teams and the trade unions about how we can work together to deliver the best possible service for our passengers.

“In fact we already have a meeting in the diary with the RMT which makes today’s announcement very premature.”

South Western Railway took over services in the south west on August 20.