The fault comes amid strikes by members of the National Union of Rail, Maritime and Transport Workers (RMT)Credit:Kirsty O’Connor/PA Newly-refurbished trains have been pulled from service over fears they are accidentally turning signals red or yellow.South Western Railway (SWR) reintroduced the 30-year-old Class 442 trains in June after giving them a £45m upgrade.But they have now been taken out of service as a precautionary measure amid concerns they are adversely affecting line-side signals.Class 442 trains, which are nicknamed ‘plastic pigs’, have been running on routes from London to Bournemouth and Portsmouth.They are thought to be incorrectly turning signals red or yellow as they go through Earlsfield station in south west London.Train signals are a traffic light system used on railways. They ensure trains are kept a safe distance apart and take factors such as stopping distances into account. SWR are working with Network Rail to correct the issue but have confirmed that two services will need to be temporarily cancelled – a morning service from Southampton Airport Parkway to Waterloo, and an afternoon service from Waterloo to Poole.Shorter trains will also run on five daily services between London and Farnham, Guildford, Haslemere and Woking, SWR said.”We appreciate how inconvenient this will be to passengers on these trains and are sorry for any inconvenience caused,” the company said in a statement. The fault comes amid strikes by members of the National Union of Rail, Maritime and Transport Workers (RMT). Workers staged a four-day walkout on Friday as part of a long-running dispute, which began in November 2017, over the future of train guards on new driver-only operation trains.Some 800 trains were cancelled every day, with some being replaced by buses.The RMT had accused SWR of “rowing back on their public pledges” about the future function of guards and said union members were “rock solid and united” in supporting the action.SWR said it was “committed to finding a solution” to the dispute.But angry travellers took to social media on Friday to complain about the disruption caused by the strike. “How foolish of me to think I could get into work early today,” wrote one passenger.SWR, which transports more than 100,000 passengers every day, runs services between London and Bristol, Exeter, Portsmouth, Reading and Weymouth.The latest strike chaos comes after it was revealed that season ticket prices will increase by 2.8 per cent next year, significantly increasing the cost of long-distance commuting. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.