The National Railway Museum (NRM) in York has revealed that work to restore the historic Flying Scotsman locomotive is set to take longer to complete than it initially anticipated.

The future of the iconic No.4472 locomotive was secured by the attraction with the support of the National Heritage Memorial Fund in 2004, while a £250,000 campaign was launched last year in order to fund the restoration.

It is hoped that the Flying Scotsman, which was withdrawn from use on the East Coast main line in 2006, will be returned to public operation on the route once the restoration scheme is complete.

However, the NRM said its "meticulous approach" and the necessary repair or replacement of locomotive parts had led to delays in the restoration scheme. It is now hoped that the programme will be completed in spring 2011.

Chris Beet, NRM engineering and rail operations manager, said: "In order to fully restore Flying Scotsman, we had to disassemble the entire locomotive and begin examining every little piece. We then decided whether these pieces need to be repaired or replaced - both options being incredibly time consuming."