The billionth seed to be collected for safekeeping and conservation by plant experts in Sussex is to be presented to Chancellor Gordon Brown.

The event is in advance of an official banking ceremony at the UK's Millennium Seed Bank in Haywards Heath on May 22.

The Millennium Seed Bank Project (MSBP), part of the Royal Botanic Gardens, is widely regarded as one of the most ambitious conservation projects in the world.

Conceived after the first Earth Summit in Rio in 1992, the MSBP is based on three central tenets of the Convention on Biological Diversity - conservation, sustainable use and equitable sharing of benefits.

The project holds the largest wild seed collection in the world and works with more than 100 partner organisations in 50 countries forming a global network to provide an effective, low-cost insurance against the loss of species in their natural environments.

The Millennium Seed Bank currently contains the seeds of more than 18,000 wild plant species from 126 countries, including 88% of the total UK flora, with duplicate collections in partner seed banks worldwide.

By 2010, 10% of the world's wild flowering plant species totalling 30,000 species will be banked, with priority given to those which are endangered, rare or of current local use or potential economic use.

The Millennium Seed Bank has the capacity to store seeds from up to half of the world's wild plant species and each one of these seeds has the potential to one day become a plant.

The billionth seed is from an African bamboo, and was collected in Mali, West Africa.

This variety is used for house building, furniture, basket and wine making. The bamboo is valuable to local people but over-harvesting has led to the species becoming endangered in Mali.