RMT members at Northern Rail and Greater Anglia strike
Workers at two train companies have walked out again in a dispute over the role of guards.
Rail, Maritime and Transport union (RMT) members at train operators Northern Rail and Greater Anglia have staged a 24-hour strike.
The union argues passenger safety would be put at risk by getting rid of guards and extending driver-only services.
Greater Anglia said it was running a normal service, but Northern services have been affected.
Northern said a majority of its services would run between 07:00 and 19:00 BST but "many routes will start to wind down from late afternoon".
RMT general secretary Mick Cash said: "It is ludicrous that we have been able to negotiate agreements in Wales and Scotland that lock in the guard guarantee, but we are being blocked from reaching the same settlement across the North and Greater Anglia."
Northern said driver-only trains are widely used elsewhere.
The company added: "We are still prepared to offer unprecedented guarantees of jobs and pay reviews until the end of our franchise in 2025, with the government guaranteeing jobs beyond that, but both guarantees depend on RMT ending its strike action."
Greater Anglia said it wanted to employ conductors, but they would "concentrate on customer service rather than opening and closing doors".
Eight MPs have called for an inquiry into the running of Northern Rail, urging the government to consider nationalising the service.
They tabled a motion describing an "appalling level of delays and cancellations", which they said would increase if plans for driver-only trains are introduced.
This latest action follows earlier walkouts in March, January and September, which also included employees of other operators, including Merseyrail, South Western Railway and Southern.
The union planned to stage a series of strikes at South Western Railway on 11, 14, 16 and 18 May but suspended the industrial action "pending talks with the operator".