A TRANSPORT authority is seeking permission to spend almost £600,000 on five new buses as it works to replace a fleet of "extremely unreliable" vehicles.

Strathclyde Partnership for Transport, which oversees bus operations in the west of Scotland, will today ask members to approve a bill for £575,000 to purchase five buses from Yorkshire-based manufacturer, Optare Group.

It takes the total bill for new buses this year to £1.15 million, after SPT approved an order for five Optare buses in January at a cost of £575,000.

The buses are used on SPT's subsidised routes, when bus operators are contractually obliged to use SPT-owned vehicles on a "full repairing lease basis" - meaning the operator must foot the bill for maintenance costs.

SPT spent some £10m between 2008 and 2013 procuring a fleet of 110 vehicles which could be farmed out to operators and cut costs to the public purse.

The bulk were supplied by Glasgow-based Allied Vehicles Ltd, with Optare providing a smaller number.

However, in 2013 SPT described 14 of the original vehicles as "extremely unreliable". Bus operators complained of soaring maintenance costs and being burdened by fines for having vehicles off-road.

The decision was taken to write them off early, although SPT stressed the original cost had been "covered by the revenue savings from tendered contracts". They were replaced by 14 new Bluebird vehicles, at a cost of £1.1m.

The remainder of the fleet - 96 vehicles - was to be replaced when they reached either seven years of age or 300,000 miles, at an estimated cost of £8.6m over seven years.

However, in January this year the mileage limit was cut to 250,000 amid mounting concerns that the vehicles were not "technically robust" enough to cope with passenger services.

An SPT report stated: "This fragility is manifesting itself in a greater incidence of component failure, including in major items such as gearboxes. These problems are increasingly affecting SPT's ability to ensure service reliability."

Despite supplying the original buses, both Allied Vehicles and Optare are on a shortlist of pre-approved manufacturers drawn up by SPT last year, along with Alexander Dennis, Wrightbus and Plastisol UK.

Patrick Harvie, Scottish Green MSP for Glasgow and bus campaigner, said: "The unreliability of Glasgow's buses has long been a serious embarrassment for our city, and it will be galling to passengers to see the need to pay for new vehicles so soon.

"It seems bizarre that the firms supplying problematic vehicles continue to be listed as approved suppliers, and I would urge SPT to seek firm assurances about the quality of the fleet they're buying."

SPT said the policy of supplying buses direct to contractors had "achieved significant budget savings in the seven years since SPT embarked on the initiative and is an initiative worthwhile continuing".