The "eight wonder of the world", as it is dubbed, will be built in a 34-acre disused Cornish clay pit which, by the spring of 2000, will have been transformed into a "Garden of Eden".

The Eden Project, near St Austell, has been partly funded by a £37m grant from the Millennium Commission, chaired by Mr Smith.

The half-mile long project will feature the largest plant house in the world, containing 10,000 species of plants inside giant greenhouse "biomes".

Each of the three biomes, covering 450,000 square feet, will contain separate mini-climates - desert, Mediterranean and humid tropics - which will demonstrate and explore the relationship between the conservation of plants and food production.

The tropical rain forest biome will be 10 metres higher than Nelson's Column in Trafalgar Square, to allow the rain forest trees to grow to their full height.

The whole project, which will provide around 300 jobs, will require more than 2,700 tonnes of steelwork.

Work began last October to fill in areas of the 250ft pit and make room for the buildings which will form part of the complex.

Thousands of plants are currently being grown at specially-built greenhouses nearby, and major work on the foundations is starting next month.