A man waits on a platform in Manchester Victoria station during a reduced transport service due to industrial actionCredit:OLI SCARFF/AFP/Getty RMT general secretary Mick Cash said: “The RMT action on Merseyrail this morning is absolutely solid, with pickets out in force at all key points and the response on the ground has been wholly positive. It has been a massively successful operation.”More than half of services on Arriva were set to be cancelled, while Southern said it aimed to run most of its 2,200 trains.The RMT strike on Southern is the 30th since a row over the role of conductors flared almost a year ago. Services were further reduced when drivers refused to cross picket linesCredit:OLI SCARFF/AFP/Getty The RMT revealed it was considering legal options over “failure” of the Office of Rail Regulation to protect the rights of disabled passengers on Southern.Officials said their concerns arise from reports from members and passengers that disabled passengers on Southern are being treated less favourably than other passengers as a result of the company’s decision to end the guarantee of a guard on new driver only services. Members of rail staff taking industrial action hand out leaflets to passengers on Monday morningCredit:OLI SCARFF/AFP/Getty Unions have argued that the changes mean conductors will be sacked, but rail operators have vowed this is not the case. Theresa May’s official spokesman said the Prime Minister was “disappointed … that once again the RMT are disrupting passengers across the country”.The spokesman said: “These strikes are unnecessary. The RMT should return to talks and help deliver the high-quality rail services that passengers deserve.”Beverley and Holderness MP Graham Stuart warned the strikes will anger commuters because the changes are not scheduled to be introduced on northern services for several years. The union mounted picket lines outside stations, saying they were receiving support from the public for its campaign to keep a safety-critical guard on trains.Merseyrail had hoped to run almost half its services, but a number of drivers refused to cross picket lines. The company said it was running around 20 per cent of services, far fewer than previously advertised.Trains were still running on most routes, every half an hour, but they were not stopping at every station. Andy Heath, of Merseyrail, said: “It is unfortunate that many drivers took the decision not to work today.”This is bad news for the travelling public within the Liverpool city region and the local economy, both of which will suffer as a result of today’s strike.” General secretary Mick Cash said: “It is obviously the case that if a disabled passenger once had the guarantee of a guard on their service and that guarantee is withdrawn then the disabled passenger has been disadvantaged.”Far from being about modernisation, driver only trains turns the clock back on the rights of disabled and older passengers.” Up to 2,000 members of the Rail, Maritime and Transport union at Southern Railway, Merseyrail and Arriva Trains North are walking out for 24 hours in a growing row over the role of conductors, threatening some of the worst disruption since the industry was privatised.Worse disruption that expected was caused when train drivers refused to cross picket lines set up by other workers on Monday morning. Rail strike action has spread across the north of England as train drivers walk out over an ongoing dispute about changes to jobs, prompting MPs to brand the decision “premature” and “frustrating”.The preemptive action is part of a broader union movement instigated on the Southern network after the company introduced plans to allow drivers to operate the doors as passengers get on and off, removing the need for a guard onboard. Northern Rail train tickets will be valid on Arriva buses in the North West to help passengers during RMT industrial action-13 March. pic.twitter.com/LRdn78cKNV— Arriva North West (@arrivanorthwest) March 9, 2017 Monday’s strike action hit Southern Railway, Merseyrail and Arriva Trains NorthCredit:OLI SCARFF/AFP/Getty, Peter Byrne/PA David Sidebottom, director of the independent watchdog, Transport Focus, said: “These industrial relations problems are being dumped on passengers who may have to cancel plans or endure miserable journeys. It is crucial that all parties have discussions to resolve this matter without bringing the railway to a standstill.”Mr Stuart MP said: “The union’s action is totally premature as it has not yet undertaken detailed discussions with Northern Rail about its plans for the future of the service and local people and businesses will be baffled and frustrated that they are the ones being inconvenienced.”The sensible thing to do in these circumstances would be for the union to talk to the train operator about its concerns rather than seek to grandstand in this way. Jumping the gun with strike action won’t resolve anything and it certainly won’t win public sympathy for their cause.” The union said the ORR has not made a completed assessment of the effects on disabled passengers of removing the guarantee of a guard prior to Southern implementing its changes at the start of the year. We advise checking our Twitter feed before travel on Monday for latest updates regarding strike action. https://t.co/f6BRjqv14K pic.twitter.com/W3w5SHJeoK— Merseyrail (@merseyrail) March 10, 2017 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.