The Woodland Trust has underlined the seriousness of the outbreak of deadly ash dieback as more infected sites are discovered.
A spokesman for the Forestry Commission has revealed that there are more than 20 suspicious sites.
The disease has also been identified in Scotland. Ash trees account for 30% of the UK's forests and the Chalara fraxinea fungus, which causes ash dieback, has already killed 90% of ash trees in Denmark.
A ban on the import of ash trees comes into force today. There are fears that the disease could devastate the UK's ash tree population in the same way elm was wiped out in the 1970s by Dutch Elm Disease.
Andrew Sharkey, Head of Woodland Management for the Woodland Trust, said: “Losing ash within the UK landscape would have serious implications to both the ecology, culture and landscape of our countryside.
"This is yet another example of why the protection of our native trees, natural resources and eco-systems needs to be at the top of the agenda and we need a step change in the level of importance placed on bio-security to tackle the bigger issue.
"The occurrence of tree diseases in the UK is becoming far too frequent and once they are established we are often powerless to act.”
“We are potentially facing the ash equivalent of Dutch Elm Disease, and unless we take serious measures as a country we will continue to see problems arising from imported diseases.”
Labour has accused the Government of acting too slowly in banning imports. Shadow Envionment Secretary Mary creagh said:
"The Government have been asleep on the job with ash dieback. They discovered the disease in a tree nursery in February but waited until it was found in the wild in August to consult on banning ash imports.
"The government also ignored the Forestry Commission's warning that there was no money to tackle tree disease and cut its cash by 25%, forcing seven offices to close and cutting 250 staff. You simply can't trust this incompetent Tory-led government with the nation's forests."
Mr Sharkey said:
“If this was a case of foot and mouth there would be immediate emergency measures put in place to deal with it. We need an emergency task force or summit set up by Government immediately to help deal with current threats and to stop any future threats before they arrive in the UK.
"We must focus our minds, time, and resources towards these issues and the Government has to act on its own Action Plan for Tree Health and Plant Bio security plan which states that protecting the UK through import controls is a priority. If ever there was a time when we all need to work together for the future of the countryside this is it.”