Image copyright RMT Image caption RMT general secretary Mick Cash (centre) visiting pickets in Colchester

Train passengers face another day of disruption as union members at four rail firms stage the latest 24-hour strikes in disputes over safety.

Services on Greater Anglia, Merseyrail, Northern and South Western Railway, including its Isle of Wight Island Line, are likely to be affected on Wednesday.

RMT union members also walked out on Monday and plan to again on Friday.

The Department for Transport denied the dispute was about safety.

It said rail companies would "keep passengers moving".

Image copyright PA Image caption During Monday's strike, commuters packed on to a South Western Railway train on the Portsmouth to London Waterloo line

The disputes the union has with rail firms include concerns over the role of guards, fears over safety and job losses surrounding plans to introduce new driver-only operated trains.

RMT union members have been told not to book shifts between 00:01 and 23:59 GMT on strike days.

Services during strike action:

Greater Anglia said it was "very disappointed that the strike is going ahead" and plans to run a full service

Merseyrail said "unfortunately" it would run a reduced service in and around Liverpool between 07:00 and 19:00, but with a break during the middle of the day. There will be no trains on Kirkby, Ellesmere Port or Hunts Cross lines

Northern, which covers north-west and north-east England, said it was "focusing on running as many trains as it can" and will operate about 1,350 trains on strike days - roughly 60% of its normal services between 07:00 and 19:00

South Western Railway, which operates in areas including London Waterloo, Reading, Exeter and Southampton, said it had "offered assurances around the need for more guards in the future" and planned to run about 70% of its normal services, while there would be bus replacements on its Isle of Wight Island Line

Image copyright PA Image caption Commuters were able to travel on Greater Anglia's train at Shenfield in Essex on Monday as it ran a normal service

RMT general secretary Mick Cash said: "Our members are standing firm this morning in the separate disputes across the country in defence of rail safety and the role of the guard.

"This week, in the midst of the Tory reshuffle shambles, we called on Transport Secretary Chris Grayling to organise summit talks to move these disputes forwards. We have had no response.

"Mr Grayling's silence speaks volumes and, with today's damning NAO report into the Southern Rail fiasco, it is becoming clearer by the minute that all the Tory government are interested in is protecting the fat profits of the greedy private rail companies regardless of the impact on services and safety.

"The strikes today are about putting public safety before private profit."

Mr Cash said the agreements had been reached in Scotland and Wales to keep guards on new modern trains.

A Department for Transport spokesperson said: "This is a dispute between a private company and the RMT. However, the Transport Secretary recognises the disruption caused to passengers and has met with union leaders on several occasions, including as recently as December, to help bring an end to the strikes.

"He offered guarantees of employment to members who currently fulfil the role of the second person on the train beyond the length of the franchises - instead the RMT called strikes on five train companies to cause maximum disruption to passengers.

"Nobody is losing their job as a result of driver-controlled operation trains - employees have been guaranteed jobs and salaries for several years."