Built in 1864, the ship made annual runs from London to South Australia carrying thousands of migrants and supplies for the growing colony.

An estimated 250,000 South Australians can trace their origins to passengers who sailed to Adelaide on one of the clipper's 23 trips.

It now sits in a slipway in Scotland and the Scottish Maritime Museum has called for tenders to demolish it.

Among those to back calls to save the ship are South Australian Governor Kevin Scarce, former foreign minister Alexander Downer, Liberal senator Nick Minchin, former South Australian premier John Bannon and Adelaide Lord Mayor Michael Harbison.

Their letter describes the City of Adelaide as an extraordinarily important part of both Australia's and Great Britain's heritage.

"As the only surviving sailing ship built to give regular passenger and cargo service between Europe and Australia, she represents a whole foundation era of Australian economic and social history," the letter says.

"It is difficult to imagine a more vital icon of the making of modern Australia and of the relationship between Britain and the Australian colonies.

"We especially urge the people of the United Kingdom to ensure that this grand lady of the days of sail is not demolished and broken into pieces."

The City of Adelaide Preservation Trust, which instigated the letter to the British PM, said its objective was to move the ship to a temporary location in the UK at a cost of $1.5 million.

"Ultimately, we wish to transport the vessel to Adelaide and this can be undertaken for a further $2.5 million," said naval architect Peter Roberts.

"But our first priority is to ensure it is not demolished."

Mr Roberts said contrary to some reports the clipper was not in disrepair and rotting.

"This is definitely not the case and until the 1980s, it was used as clubrooms for the local naval reserves," he said.