Unofficial industrial action by train drivers is expected to close Glasgow's underground system on Wednesday.

The dispute involves about 40 drivers who are angry about extra duties they have been asked to take on.

They have been asked to help train new drivers who will do additional duties like monitoring CCTV cameras.

The strike plan has been condemned by Strathclyde Passenger Transport (SPT), which operates the underground system.

Moray MacDonald said talks lasted 12 months

The action is expected to begin at 0530 GMT on Wednesday when the first shift of the day clocks in, although SPT bosses have begun to make contingency plans.

Drivers warned they would strike for 24 hours if they were asked to train new drivers on Tuesday.

SPT confirmed drivers were asked to help out with training and the strike was called.

SPT spokesman Moray MacDonald said: "We've been in discussions for over a year with the union and we've been discussing various options and we've made various recommendations.

"Now they are refusing to undertake training duties which are part of job descriptions and they have no intimated that they will walk out in refusing to do that."

About 55,000 people use the subway every day and posters at underground stations will advise them about bus routes, including extra shuttle services.

It is understood the Transport and General Workers Union is against the illegal action, but it is not known at this stage whether it will be able to dissuade members from striking.