An engineering workshop in the Scottish town of Kilmarnock may seem an unlikely place to find the answer to Oxfordshire commuters’ prayers.

However, work being carried out there will soon ease the squeeze on busy rush-hour trains serving the county.

Extra 125mph rolling stock for train operator First Great Western is being overhauled or converted in Kilmarnock by Wabtec Rail Scotland, which can trace its roots back to a business founded in the town in 1840.

Five five-coach Class 180 Adelante express trains, last used by FGW in 2009, are being given a makeover before they return to operation on services between the Cotswold Line, Oxford and London.

And 15 redundant buffet cars are being turned into standard class passenger coaches, which will add an extra 84 seats to many of FGW’s High Speed Trains used on services from Oxford and Didcot.

Last summer the Department for Transport revealed that the 10 most overcrowded commuter trains operating around London were all FGW services to or from Paddington station, including four serving Oxfordshire.

Although work by Network Rail to electrify the Great Western main line to Oxford is expected to start next year, bringing the prospect of new and cascaded electric trains from 2016, finding a way to boost capacity in the short term on FGW’s currently diesel-worked routes was not easy. Lengthy negotiations with the DfT eventually led to a deal for the extra stock last autumn.

Speaking to the Oxford Mail in Kilmarnock, FGW managing director Mark Hopwood said: “We had to find a way to add capacity quickly on a railway facing electrification, which meant it was difficult to justify new-build trains.

“The vast majority of the extra capacity will be delivered by the summer, ready for the Olympics, to cope with the additional passengers then.”

He added: “Our customers will see a big increase in the number of seats at the busiest times of the day but there is more to come.

“This is a short-term project but is part of a long-term effort to raise capacity on Great Western routes.

“The return of Adelantes to the Cotswold Line will be a good step up in journey quality for our passengers, with all but one train running west of Moreton-in-Marsh on weekdays operated by an Adelante or an HST.”

FGW stopped using the trains due to concerns over operating costs and technical problems but Mr Hopwood said that the Adelantes used by sister firm First Hull Trains were now as reliable as FGW’s HST fleet.

All 14 Adelantes in use with UK train operators are being given reliability modifications by their owner Angel Trains in a £5m programme.

Wabtec Rail Scotland site director Craig Gibson said the work being carried out by his staff would give the Adelantes and extra HST coaches the look and feel of brand-new trains, matching FGW’s existing express fleet.

John Ellis, the chairman of the Cotswold Line Promotion Group, which represents passengers on the route, said: "The CLPG welcomes the impending reintroduction of Class 180 Adelante trains on the line.

"These trains provide a hugely improved standard of environment compared to the suburban Turbos which they will replace. Seats are more spacious and comfortable, there will be proper air conditioning and decent toilet facilities. They have a top speed of 125mph and better acceleration. They are the right trains for the Cotswold Line."

Overhaul checklist

Class 180 Adelante: The trains are stripped of interior fittings before being repainted inside and out in a process which takes three days per coach. New carpets and seat covers are being fitted, along with power sockets for laptop computers. The first set is expected in service in May, and all five should be in use by late July. The Turbo trains they displace from Cotswold Line duties will be used to add extra coaches to busy peak trains on the Oxford-Reading-London corridor.

HST buffet car conversions: The coaches are stripped of all fittings and given corrosion repairs before being repainted. New seats, lights, toilets and luggage racks are fitted. The removal of redundant kitchen equipment means the finished coaches will be five tonnes lighter than they were in their old role. The first five will be delivered to FGW in July, just in time for the London Olympics, with all the rest in traffic by September.