ScotRail have apologised to passengers after complaints over "freezing" temperatures on some Helensburgh and Lomond train services.

Customers claimed the on-board temperatures on some West Highland line services - calling at Helensburgh Upper, Garelochhead, Arrochar & Tarbet, and Ardlui - sometimes dropped as low as 2.5 degrees Celsius.

One particular train which attracted criticism was the 5.17am from Oban to Glasgow Queen Street - the only one on the route that gets travellers into Glasgow city centre before 9am.

One passenger complained of old trains, leaking doors and windows and broken or inadequate heaters, according to the Daily Record. 

ScotRail attributed the problem to the time taken to heat up the carriages before the first service of the day.

They also cited issues around staff availability as well as - in the case of West Highland services - noise concerns in Oban and Mallaig preventing them starting up the trains' engines too early in the morning.

David Lister, ScotRail's safety, engineering and sustainability director, said: “We’re sorry to customers who have experienced discomfort during their journey as a result of cold temperatures on board our trains in the West Highlands.

“We know that the Scottish winter can make heating the first train of the day before departure very challenging.

“Our staff are working tirelessly to ensure our trains are operating as reliably as possible.

“We continue to look into longer-term solutions and funding options which could improve on-board temperatures for our passengers.”

ScotRail says it carried out a comprehensive maintenance check this year to make sure the heaters are working correctly which they say has resulted in improved customer comfort.

The operator says its drivers have also been informed about using the engine’s pre-heat function which can improve the time taken to warm the trains.

In the long term, ScotRail say they will continue to look into funding a replacement of the heating system, but warned of the high cost of such a move.