One of the UK's most important industrial treasures is in danger of destruction unless millions of pounds can be raised to preserve it, its trustees have warned.

Volunteers looking after Isambard Kingdon Brunel's iron steamship the SS Great Britain say it is in danger of rusting away within three years unless vital restoration work is carried out.

The ship, which was launched in July 1843, was the world's first ocean-going, iron-hulled, propeller-driven steamship, and a forerunner to all modern ships.

But its hull has now rusted to less than half its original thickness, and its trustees say the damage will be irreversible if it is left to rot any further.

They are hoping to raise �7m to save the ship.

Essential work

They have asked the National Lottery Heritage Fund to help out with the project which will be launched next year to coincide with the 30th anniversary of the ship's return to Bristol from the Falkland Islands, where it had been used to store wool for 33 years.

Since it was brought across the Atlantic, the ship has been lovingly restored to become one of the city's major tourist attractions.

But a spokeswoman for the trustees said essential work on the hull was necessary to save it for the next century.

She said: "Iron ships like this were not built to last 160 years.

"The hull was an inch thick when it was built but it is half that now.

Crimean War

"As the iron gets older it rusts faster and we have been told that once it gets to less than 30% of its original thickness the hull will no longer be viable."

The ship's trustees say part of the �7m would also be used to secure the ship's long-term future by enhancing the facilities around its mooring in Bristol's docks.

About 100,000 people tour the SS Great Britain annually and earlier this year it welcomed its four millionth visitor.

Last month it was named one of the country's most important maritime treasures by the National Historic Ships Committee.

During its service, it carried British troops to the Crimean War, took the first ever touring England cricket team to Australia, and started the tradition of luxury ocean-going liners.