The original Flying Scotsman was built in 1923

Delays in building an Edinburgh visitor centre for the 80-year-old steam-driven machine have prompted the sale.

Two American bidders have already voiced an interest in the The A3 class loco designed by Sir Nigel Gresley.

The Flying Scotsman currently pulls the Venice Simplon-Orient Express trains which run out of Victoria station in London.

Flying Scotsman chief executive Peter Butler said: "Naturally we are disappointed at this development, but we have been unable to make sufficient progress with the proposed Flying Scotsman visitor centre at Edinburgh."

"This is the best way forward to ensure the survival of the engine on the main line, and to protect shareholder interest.

It is likely that a number of bids will be received from overseas parties David Speight valuer

"This is not a forced sale, and we are confident the result will be in the interests of everyone involved with this magnificent example of British engineering."

The loco company has now instructed international property advisers GVA Grimley to sell the Flying Scotsman steam - or locomotive No 4472 as it is officially known.

David Speight, partner with the plant and machinery valuation team at GVA Grimley, said: "We are delighted to be handling the sale of this distinguished example of British engineering excellence.

"We expect there will be considerable interest in ensuring locomotive 4472 remains in the UK.

Completely rebuilt

"It is likely, however, that a number of bids will be received from overseas parties."

The original locomotive was made in Doncaster in 1923, remaining in main line passenger service until 1963.

It still sports the colours of the old London and North Eastern Railway in which it was made.

Bought from British Rail in 1963, the Flying Scotsman pulled packed special trains in the US before returning to the UK where it was bought by Sir William McAlpine in 1973.

For a time, music impresario Peter Waterman had a stake in the loco and it was bought in 1996 by millionaire Tony Marchington.

The loco was completely rebuilt between 1996 and 1999 and was returned to the main line with an oversubscribed "inaugural run" from London to York in July 1999.