Image copyright RMT Image caption The RMT strikes over guards have been running for two years

Workers on Northern Rail and South Western Railway (SWR) have begun a new strike in the long-running dispute over the future of train guards.

Members of the Rail, Maritime and Transport Union (RMT) stopped work for 24 hours at midnight.

Northern said the action would hit Manchester's Christmas markets while SWR said it was causing "misery".

The RMT said "Britain's violent and dangerous railways" should always be staffed by "safety-critical" guards.

Northern Rail said a third of normal services would operate on Saturday.

Image copyright PA Image caption The dispute has affected commuters and rail firms nationwide

It warned no late trains will be available after music concerts including Jess Glynne in Manchester, Rick Astley in Liverpool and the Courteeners in Leeds.

SWR said it would run about half of normal services, with no trains on some routes.

It added rugby fans should allow extra time to reach Twickenham for England's match against Japan.

Image caption Picket lines have been held outside many railway stations including in Newcastle

Previously the union has called for a guarantee that trains will not run if no guard is available, while SWR has said they would run in "exceptional circumstances".

The RMT has been involved in a two-year dispute with several rail firms over the issue.

It previously said it had secured "guard guarantees" in Wales and Scotland as well as on a number of English franchises.