Professor Ian Boyd, who heads the government taskforce battling the ash tree crisis, has warned that the fungus spreading across Britain's countryside could have disastrous ecological consequences.
The chief scientific adviser at the Department for Environment, Food and Rural Affairs told BBC Radio 4: "Ecologically it is going to change the countryside very significantly. Parallels have been made with Dutch elm disease of the 1970s. This is not good."
In the UK, ash trees make up around 30% of the wooded landscape, across woodlands, hedgerows and parks.
The fungus - which causes leaf loss and can lead to the death of the tree - wiped out 90% of ash trees in Denmark in just seven years and is becoming widespread throughout central Europe.
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It will be a chilly day for many parts with the highest temperatures, about 10 Celsius (50F) in the far northwest.