THE troubled restoration of what is arguably the world’s most famous loco is to be completed – despite fears the plug could be pulled on the costly project.

Industry insiders claimed earlier this year that the overhaul of the Flying Scotsman could come to an abrupt halt because of the ever-escalating cost of the complex work.

But following the publication of an independent engineering report bosses at the National Railway Museum in York have decided to continue with the project – although not in their own workshops.

Instead they have decided to tender for an external contractor better suited for some of the heavy engineering involved.

And the timescales involved with the tender, contract negotiations, restoration work and testing mean that Flying Scotsman will not operate on the mainline before 2015.

The museum acquired the loco in 2004 at a cost of £2.3m and when restoration began in 2006 it was estimated the work would cost around £750,000.

But the project – possibly the most complex of its kind ever undertaken - was beset with problems and by the end of February this year the cost of the work had spiralled to £2.89m – with substantial further spending still necessary.

The report from engineering consultants First Class Partnerships recommends that the middle steam cylinder needs realigning, requiring the removal of the boiler and all three steam cylinders. All three steam cylinders are also oversize and need to be fitted with new liners and rebored.

Part of the loco cannot be examined until the steam cylinders are removed – and a final assessment of the viability of the restoration will be made once the condition of the main side frames is known.

However the report said the risks of any further serious problems were small and the cost of overcoming them relatively low – although the contract would include a “break clause” just in case.

Museum director Paul Kirkman said: “It was vital that we really got to the bottom of this complex project and received independent verification of the problems associated with the locomotive and how best to complete the project.

“We have now clarified that it is not sensible to complete the work in-house and are in a position to go out to tender for an external contractor.”

Museum bosses are reluctant to put a price on the remaining work in order not to prejudice the tender process but in January the magazine Steam Railway claimed it could be in the region of £500,000.

However the cost will not be met by public appeal – and will instead be met by the Science Museum Group, of which the NRM is part.