Hailed as one of the most important conservation projects ever, after eight years of planning, building and stock-piling, it is finally throwing its doors open to the public.

The Millennium Seedbank project aims to amass and store billions of seeds from across the world before the end of the decade, providing a unique resource for future generations.

With more than 300 million seeds currently in storage, the project has already collected every single type of UK flora and is well on the way to its goal of gathering ten per cent of the world's flowering plant species by 2010.

Funded by the Millennium Commission, the Wellcome Trust and communications firm Orange, the £87 million project - based at Wakehurst Place, near Ardingly - has attracted support and interest across the world.

On the Saturday of the August Bank Holiday weekend, the doors of the Millennium Seedbank Exhibition will be thrown open to the public.

The exhibition aims to give visitors an idea of the crucial role played by plants in our everyday lives, and convey an impression of the diversity of seeds and the magnitude of the collection task.

Visitors are greeted by a massive seed wall, showing seeds from across the world.

Spokesman Trevor Butler said: "Some - like orchid seeds - are no bigger than specks of ash, and others are huge. The double coconut is the size of two big watermelons."

Hugh Pritchard, head of research, explains: "We have had to get on and do something very quickly because the projected loss of species over the next 50 years or so is really worrying. If the current trend continues, half of the palm species worldwide will be condemned to extinction within the next 50 to 100 years.

"The project is about conservation, but it is also about utilisation. For example, 25 to 30 per cent of all drugs either have a natural plant product in them or contain chemicals which are synthesised from natural products.

"Some of this material will be screened for components for potential medical use in the future.

"But also, there may be other uses in the future that we don't even know about yet. We can't afford to lose these plants."

The project has secured £30 million from the National Lottery-funded Millennium Commission, as well as around £57 million from other sources, and Dr Pritchard says it is worth every penny.

"This is a millennial project that was intended to take us forward into the next century. Thirty million pounds is the equivalent of a fighter jet, which makes an interesting comparison.

"It is also the equivalent of the transfer fee for two Premier League football players. For a global project of this nature, the cost of two football players seems worth it."

The exhibition is open from August 26 at 10am and will be free for visitors to Wakehurst Place. Non-members of the National Trust will have to pay £5 (£3.50 concessions) to visit the house and gardens.