[S]cientists are now saying it has been in the country for more than a decade.

Clive Brasier, a former Government adviser on forestry, said the fact that 121 of the infected sites are mature trees in the wider environment, rather than in nurseries or recent plantings, suggest that the disease has been spreading for years.

The disease will only spread the year after the tree has been infected. Prof Brasier, who continues to advise the Forestry Commission in his role as emeritus Mycologist at Forest Research, said foresters will have assumed trees showing signs of infection were suffering from other diseases or frost damage.

“It will not have been spotted because people would have thought it is wind, frost damage, other diseases or even squirrels.”