UNIONS have said they are appalled that high-speed trains being brought into service in Scotland will dump human waste onto train tracks.

A deal between unions and the Scottish Government scrapped the practice by December 2017 but a shake-up in the ScotRail fleet is expected to lead to its return.

The RMT union said the practice, would result in its members being "sprayed with human waste".

With newly-refurbished trains being delayed by supplying firm Wabtec, some older trains are being used as an interim measure to cover services which do not have tanks to store the waste.

The RMT general secretary, Mick Cash, has written to the company’s managing director, Alex Hynes, and the Scottish government transport secretary, Michael Matheson, calling for urgent action on the issue and highlighting the “serious health risks” posed.

East Kilbride Connect: Mick Cash, general secretary of the Rail, Maritime and Transport Workers Union

Manuel Cortes of the transport staff union TSSA added: "We must bring this unhygienic and disgusting practice to an early end as no one should be working surrounded by excrement."

ScotRail described the situation as "far from ideal".

Currently the only route that has a train fitted with a waste tank is the service running between Aberdeen and Edinburgh.

RMT general secretary Mick Cash said: "Our members are rightly appalled that ScotRail have sought to rip-up a clear agreement to end the filthy and disgusting practice of dumping human excrement on Scotland's railways.

"This disgraceful and retrograde step must be halted now and the union will take whatever action is required to hold ScotRail to their agreement with the union.

"One minute ScotRail are bragging about their aim to operate the most modern railway in the world and the next they are back to spraying track workers with human waste."

A ScotRail spokesman acknowledged that it was likely to be some time before newly refurbished trains with human waste tanks would be ready.

In a statement, the company said: "We are working flat out to get more upgraded trains into service as quickly as possible, but our supplier, Wabtec, is behind schedule and has let us down.

"To ensure we can deliver services for our customers we will introduce classic high-speed trains until enough upgraded Inter7City trains are available.

"These classic trains will not have retention tanks, which is far from ideal. We are doing everything we can to mitigate this as soon as possible."

A Transport Scotland spokeswoman said: “We understand this interim measure is regrettable, but necessary to support more services and jobs across the country while retaining passenger services between our key seven cities.”