A groundbreaking plan to store the world’s plants in seed banks to prevent them from extinction has hit a snag after scientists discovered one third of endangered species cannot be frozen.

The Millennium Seed Bank, set up by the Royal Botanical Gardens at Kew is the world’s largest and most diverse genetic ‘ark’ and is on track to have collected 25 per cent of global species by 2020 as part of a wider scheme with institutions around the world.

But new research by Kew scientists has found that the seeds of a huge number of endangered species simply cannot survive the process of drying and deep freezing.

It includes some of Britain’s most beloved trees such as the oak, horse chestnut and sweet chestnut, which are in danger of dying out because of invasive moths.

John Dickie, from Kew's Millennium Seed Bank and one of the authors of the paper, said: "Ex-situ conservation of plants is more critical than ever, with many threats to plant populations including climate change, habitat conversion and plant pathogens, we need to make sure we're doing all we can to conserve the most important and threatened species.

"As successful as seed banking is for some species, it is not suitable for all seed plants and we need to invest in other ways to safeguard seeds.