Official: England's forest sell-off will cost more than it saves

Selling off England's public forests could cost the nation more than it would save, according to an official government document that emerged last night.

The Coalition Government's own impact assessment cast doubt over claims by ministers that the controversial sale would raise between £140m and £250m, helping the Department of the Environment, Food and Rural Affairs (Defra) meet its spending cuts target.

Labour, which has called a Commons debate on the issue today, claimed the document should force ministers to think again. Mary Creagh, the shadow Environment Secretary, said: "The devil is in the detail of these proposals. Defra's own impact assessment reveals that every option for selling the forests costs the taxpayer more than keeping them in public ownership. This shows that the Government's proposals are economic as well as environmental madness."

According to the Defra report, the proposal to transfer heritage forests – including the New Forest in Hampshire and the Forest of Dean in Gloucestershire – to a conservation charity would cost £507.9m but yield benefits of only £495.9m. Although the value of these woodlands on the open market is estimated at £220m, the report describes them as "unsellable at a political and practical level" and says the option is therefore "unviable".

Selling or leasing the large-scale commercial woodlands would cost between £579.1m and £748.7m but yield benefits of between £573.1m and £737.8m, the document says. Selling the other "community woodlands", valued at £50m, would involve costs of £234.1m and bring in benefits amounting to only £231.9m.

Ministers confirmed the raw figures but disputed Labour's interpretation of them. They said the cost-benefit analysis included short-term transitional costs of transferring forests but could not at this stage estimate long-term benefits such as private-sector operators running them more efficiently than the Forestry Commission.

A Whitehall source said last night: "This is another example of Labour deliberately putting misinformation out there. The impact assessment has always been freely available alongside our consultation.

"It is simply not true to say costs outweigh benefit – as an explanation of the up-front transitional costs involved and additional economic benefits down the line makes clear."

According to online campaign group 38 Degrees, more than 367,000 people have signed a petition to save the forests, with more than 51,000 writing to their MP demanding woodlands remain in public ownership.

Ms Creagh appealed to the 37 Tory and five Liberal Democrat MPs with more than 1,000 hectares of public forest in their constituency to listen to public opinion by voting with Labour at the close of today's debate. She told them: "The wholesale sell-off of England's forests now proposed by your Government was not mentioned in either your general election manifesto, or the Coalition Agreement. There is no political mandate for such a sale."

In Wales, Elin Jones, the Rural Affairs minister, has asked the Forestry Commission to adopt a "more commercial" approach but ruled out a widespread sell-off. She plans to "compensate" the public by buying new land for planting or management if any forest is sold off.