The English oak is under grave threat from a little-understood new disease that forestry experts fear is spreading far more rapidly across the country than previously estimated. Acute oak decline (AOD), which is thought to be caused by a previously unknown bacteria, causes trees to 'bleed' black fluid and kills them within five years. So virulent and lethal is the infection that foresters believe it could devastate the countryside and urban green spaces even more than Dutch elm disease, which has killed 25 million trees in Britain since 1967. The Forestry Commission has identified 55 sites across southern England, the Midlands and East Anglia which have been infected so far. But woodland groups believe it has already spread to hundreds more locations and accuse the Government of starving scientists of the funds to research the disease, which only became widely recognised in the past two years. Peter Goodwin of Woodland Heritage, one of a coalition of 10 conservation and business groups asking for �10m over the next five years to find a cure, said: "This is a truly frightening disease. It has the potential to cause the death of oak trees on a massive scale and it seems to be spreading quickly � evidence suggests it has gone way beyond locations identified by the Forestry Commission. "We're looking at a disease that has the potential to change our landscape even more than Dutch elm disease, and yet nothing is being done. We cannot afford a repetition of what happened then. Hilary Benn, [the Environment Secretary] has known about this for months and yet the scientists trying to find out how the disease works are desperately short of funding." Experts say that, as well as spreading towards North Wales and threatening the West Country, the disease is beginning to attack the country's ancient oaks, some of which have lived for more than 400 years. It has been found in Staverton Thicks, a woodland near Woodbridge, Suffolk, where some pollarded oaks date back to the 18th century, and Hoddesdon Park Wood, an ancient forest in Hertfordshire.