The biggest rail workers’ union has set a deadline for agreeing a deal to end one of the long running disputes over the role of guards on trains.

The move by the Rail, Maritime and Transport union followed a meeting to discuss the row with Merseyrail, which has been running for over a year.

A joint statement from the RMT, Merseytravel and the Metro Mayor Steve Rotheram said: “The meeting was scheduled to enable an update on the Acas process to date from the RMT’s perspective and we discussed the next phase of the negotiations.

“Today’s discussions have been positive and constructive and we have made good progress in agreeing a roadmap for further discussions and meetings as we work towards a mutually agreeable solution to the dispute.

“All parties are agreed that, whilst these further discussions take place, we will maintain the confidentiality agreed at Acas until we have agreed further public statements.”

RMT general secretary Mick Cash added: “RMT is writing to Merseyrail tonight giving them until August 31 to agree a deal in principle that underpins the guard guarantee.”‎

The union recently agreed a deal with Greater Anglia to end the guards’ issue but remains in dispute with Southern Railway, Arriva Rail North and South Western Railway (SWR) as well as Merseyrail.