TRADE union leaders have blasted the ScotRail operator over "shambolic" industrial relations which have forced a third of Sunday train services to be cancelled due to a lack of drivers.

Members of the train drivers' union Aslef are in dispute with bosses over pay and plans to slash the number of conductors on trains, which they say threatens safety.

Grahame Smith, General Secretary of the Scottish Trades Union Congress (STUC) said: "It is simply astonishing that significant service reductions are being announced only three months after Abellio assumed control of the ScotRail franchise.

"Their approach to workforce planning and industrial relations appears nothing short of shambolic and contrary to the impression they were anxious to portray during the bid process.

"The Scottish Government must now answer serious questions over how service cuts and amateur industrial relations are permissible under the terms of a very detailed franchise agreement".

ScotRail relies on drivers offering to work Sundays in exchange for overtime pay, but the ongoing dispute has caused a "steep decline" in volunteers.

Union members have rejected the offer of a 2.5 per cent pay rise plus £500 bonus - reduced from a previous offer of £1000.

They are unhappy that the pay rise is tied to productivity, and by plans to switch from a seven-day working week - removing overtime pay for Sundays.

Aslef has also raised concerns over a proposal for drivers instead of conductors to operate doors on more trains, which could threaten 150 conductors' jobs on the Edinburgh-Glasgow route.

A spokesman for ScotRail Alliance, which represents Abellio ScotRail and Network Rail, said: "We have tabled an offer that delivers higher pay, less weekend working and a better work/life balance to our drivers. It also means that we can deliver a robust service on a Sunday and gives us the opportunity to grow those services in the future. We believe that this is a fair offer and we remain open to discussing it with the unions."

A spokesman for Transport Scotland said: "This is a matter for ScotRail and ASLEF and we would encourage both parties to work together to resolve their differences and avoid unnecessary disruption for passengers on Sundays."