Prospect negotiator Malcolm Currie said: “We are extremely disturbed that the government is not waiting for the findings of its own independent panel of inquiry, but is pushing ahead to sell off the family silver. It’s unfair to put highly committed, highly professional public sector workers through this level of uncertainty. It also completely underestimates the wider impact of these proposals on the whole forestry industry, which has not been consulted at all.”

The sale of 15% of land – 38,700 hectares – is the maximum legally allowed without changing the current rules. The aim is to raise £100m for the Department for Environment, Food and Rural Affairs, which itself is facing a cut of 29%.

The union’s Forestry Commission branch president Lorraine Adams said: “Yet again, the environment secretary Caroline Spelman has jumped the gun. How can she be so confident of the outcome, before the panel has barely begun its deliberations? People were sceptical of this panel from the start and this proves they are right. The loss of more than 400 jobs, and now the sale of land on top, means we will be severely curtailed in what we can offer to the public.

“It’s us, not Spelman, who will have to look into the eyes of disappointed children, climate change campaigners and the plethora of forest users to explain to them just why things aren't as good as they used to be.”

Prospect represents 270 specialists in the Commission, who do vital environmental research to guard against and combat tree diseases and monitor climate change. Other expert roles include engineers, foresters, policy writers, librarians, photographers and recreation experts.