AS commuters continued to struggle with problems caused by the £800million upgrade to Waterloo and the South West network, last week, the RMT rail workers union is threatening to add more misery to their journeys with strike action.

As the new South Western Railway franchise rolled out its new brand last Monday RMT announced workers are to vote on whether to take strike action in a dispute over the role of guards.

A ban on overtime and rest day working could be on the cards in the ballot which includes guards, commercial guards and driver members on SWR.

The threat of industrial action first reared its head earlier this summer when it emerged 90 new trains ordered by the new operator have the capacity to be driver-only operated (DOO).

Although SWR has confirmed all services will have at least two members of staff on board, it has so far refused to commit to protecting the role of train guards.

Responding this week, the RMT said it had “spent months” since First Group and Hong Kong Metro operator MTR won the SWR franchise from Stagecoach trying to get a “water-tight pledge” out of the new owners on the role of guards.

But instead it has been met with “a barrage of spin and prevarication”.

General secretary Mick Cash said : “The 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.

“This dispute can be easily resolved if the company are prepared to stick to existing agreements, give staff and passengers alike a guarantee of a second, safety-critical member of staff on all current services and an assurance that safety and access are the absolute priority.”

SWR has called the union’s actions “unnecessary”, commenting it would provide more guards and drivers, and would work with the RMT to "deliver the best possible service”.

A spokesman for the new rail operator said: “We have made it perfectly clear 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.”

Srike action on Southern Railway services across Sussex have left commuters furious and exhausted in a protracted dispute with many passenger groups calling on Government ministers to step in and solve it.

The fear of industrial action causing mayhem at the UK’s busiest terminal at Waterlook adds to SWR’s rocky start running the new franchise, which continued on Monday, as numerous faults across the network and signalling problems led to long delays and cancellations.

Speaking at the unveiling of its first fully-liveried train at Waterloo International Terminal on Monday, managing director Andy Mellors admitted he had had “a challenging couple of weeks”, but added: “We’re now looking to the future. Between now and 2024, we will be investing more than £1.2billion on new and refurbished trains, station improvement projects and the simplification of tickets.

“We are eager to roll out these improvements which will make journeys better for our customers across the network.”

As well as showing off the new brand, SWR made 100,000 half-price advanced tickets for passengers available to buy online this week.

The offer includes travel to and from areas such as London Waterloo, Exeter, Bristol, Bath Spa, Weymouth, Bournemouth, Salisbury, Portsmouth Harbour and the Isle of Wight.

Transport Secretary Chris Grayling who attended the launch, said: “This is the start of a new era for people who use the South West route. We are determined to improve journeys for passengers and passengers will benefit from faster journeys, 90 new trains and more than 50,000 extra seats in and out of Waterloo each day during rush hour. We are delivering the biggest rail modernisation programme for over a century.