By Helen Briggs
Science and nature reporter, BBC News
Britain's native toads are at risk from a deadly infection that has driven many of the world's amphibians to extinction, say UK scientists.
The common toad is known to be susceptible to infection
The fungal disease is currently confined to Kent, where it was brought in by imported frogs.
But if it spread further it could, in theory, completely wipe out the British toad population, according to research published in a Royal Society journal.
Experts want tighter controls on the aquarium trade to protect native toads.
The chytrid fungus, or Batrachochytrium dendrobatidis, BD, as it is sometimes called, infects the skins of amphibians such as frogs, toads, salamanders and newts.
One-third of all the losses in amphibian species recorded around the world are thought to be due to the disease.
Although the frogs that brought the fungus to Kent have long since disappeared, it is likely that they have left a reservoir of infection in the environment.
And scientists fear the disease is being brought into Britain time and time again through the world trade in amphibians.
"We strongly suspect BD is being introduced into the UK on a daily basis through the amphibian trade," said Dr Matthew Fisher, of Imperial College London.
"Our borders are wide open to the introduction of this infectious disease."
Dr Fisher and colleagues at the Institute of Zoology in London developed mathematical models to test what would happen if the disease found its way into breeding populations of the common toad (Bufo bufo), an amphibian which is known to be susceptible to BD.
Other amphibians, such as newts, may catch the disease
They found that the critical parameter was the length of time the fungus could survive in the environment away from its natural host.
The models show that there would be little impact on UK toads if the fungus was only able to live outside its host for seven weeks.
But, if it was able to survive in water for a year, the impact would be considerable, with severe declines in the numbers of toads, and in some cases extinction in 10 years within infected areas.
Previous research has demonstrated that the fungus is able to live for at least seven weeks outside its natural host.
But the rapid declines in amphibian numbers in areas such as Australia and South America suggest that it may linger for much longer than has so far been seen in the laboratory.
Dr Matthew Fisher told the BBC: "Under the worst case scenario, you could lose the common toad in the UK. That's highly unlikely but it has to be taken into consideration."
The research, published in the Proceedings of the Royal Society B, adds weight to calls to test all amphibians for the disease before they are brought into Britain.
The wildlife charity Froglife said it was important to make people aware of the danger to native amphibians.
"It is thought that it could have been brought to the UK by exotic pet species, such as the African clawed toad, that have escaped or been deliberately released," said a spokesperson.
"It is vital strict controls on the health of imported animals are in place to help limit the spread of this devastating disease."