The Eden Project has attracted more than 8m visitors since opening

The winner was decided by a panel of judges and a public vote and announced at the British Construction Industry 20th anniversary awards in London.

Organisers said Eden topped the Building category in the Best of the Best Major Projects because of its "influence, legacy and public benefit".

The Channel Tunnel won the other top award for Civil Engineering.

Tim Smit from the Eden Project said they were humbled to have won.

He said: "For us it has been a privilege to have been offered the opportunity to follow our dreams and build 'Eden' and to watch the engineers, architects and landscape architects weave their genius."

Eden has attracted more than 8m visitors and claims to have generated �800m for the regional economy since opening in 2001.

In December 2005, it was named Britain's favourite modern building in a poll released by Construction Skills, the sector skills council for the construction industry.

The project is made up of large greenhouse domes on the site of a former china clay pit near St Austell.