A BITTER industrial dispute between ScotRail and hundreds of conductors has soured further after the operator confirmed it was threatening legal action amid claims that further planned strikes may not be lawful.

Members of the RMT trade union have staged a series of walkouts in recent weeks, with an additional five strike days now scheduled during August. 

The row centres on the extension of driver-only operations, which RMT says jeopardises safety.

Last week the union announced that conductors would not work for 48 hours on Sunday August 7 and Monday August 8, with further walkouts planned for Thursday August 11, Saturday August 13 and Monday August 14. 

ScotRail said it would be able to operate 81 per cent of trains on strike days. 

The walkouts will affect diesel services where conductors open and close the doors. 

ScotRail said it was challenging the legality of the strikes, but RMT accused managers of "interfering in workplace democracy".

A spokesman for RMT said: "There is a threat of a legal challenge that RMT will look at in detail before we respond formally.

"This latest move shows that ScotRail are keener on interfering in workplace democracy under the cover of the anti-union laws than they are in dealing with the issues of rail safety at the heart of the current dispute."

More than half of existing ScotRail services are run on a driver-only basis, where the driver operates the doors by checking that the platform and doors are clear via CCTV in the driver's cab while a ticket examiner deals with passengers. 

The practice dates back 30 years and is expected to become the norm across the industry as new, electric trains replace older rolling stock and railway lines are increasingly electrified. 

RMT insists that DOO increases the risk of passengers becoming trapped in doors or falling between the train and the platform, as well as increasing the risk of antisocial behaviour or of disabled passengers being left without assistance since trains can legally run without a ticket examiner but not without a conductor if it is supposed to have one. 

However, industry regulator, the Office of Rail and Road, has backed DOO as safe. 

A spokesman for ScotRail said: "We have written to the RMT to challenge some actions by the Union that we believe contravene the legislation that governs industrial action. We await their response."