Can you hear the silence of the huskies? When he was rebranding the Tory party, David Cameron promised us he would lead "the greenest government ever". Since he came to power, he has broken every environmental promise he made – and then gone much further. He has opened up the coasts of Britain to the deep-sea drilling that worked so well in the Gulf of Mexico, and put a "for sale" sign outside every single remaining forest in England. Yes, as his own Environment minister puts it, Cameron is determined to "dispose of public forest" – and the timber companies and holiday parks are preparing their opening bids.

In order to raise £2bn, the Government is selling all 650,000 acres of our forests – a privatisation that even Margaret Thatcher blanched at. These are the most popular outdoor spaces in Britain. They are the last places where millions of people can go to escape their anxieties and glimpse what Britain looked like to our ancestors for millions of years. They are the site of some of our most potent national myths: what would Robin Hood say if he knew Sherwood Forest itself was now on the market? Is Cameron really taking the Sheriff of Nottingham as his role model? This is in direct contradiction to what Cameron told us he would do before the election. In 2007, talking about forests, he promised he would "take a more effective and strategic approach to safeguarding a priceless – and irreplaceable – natural asset." He said the countries that were cutting forests down were "barmy". The Government says there is no danger to the forests in selling them to timber companies and the other highest bidders. They say they will still be standing, they will be cared for as well, and the public will have just as much access. Does this match the facts?

It is true that once a company has bought a forest, it will still need planning permission to cut the woods down. This is a crucial brake. But – wait – Eric Pickles, the Secretary of State for Communities and Local Government, has just announced he is "remov[ing] the structures of control" and making it "much easier" to get planning permission across the country. Planning is being massively deregulated, just as the forests are sold.

Not every buyer will cut them down, but some will. Why do the Tories think timber companies want to buy them – to abandon the work they do in every other country on earth and become druids? Confronted with this point, the Government admits there is a "possibility of established forest being bought by energy companies who would proceed to chip it all for energy recovery" – and then swiftly insists there is nothing to worry about.

The forests that remain will be less well maintained and harder to access. The Forestry Commission looks after our woods today, and 100 per cent of it is maintained to the international Forest Stewardship Standard. By contrast, only 25 per cent of private forests in England are looked after this way. After the sale, they will become more degraded, less biodiverse and less likely to survive for the long term.

And you will find it harder to get to them. The Government says that the legislation passed in 2000 granting us all the "right to roam" will mean we can enjoy them just the same. But the public only has a right to access woodland classified as "freehold". According to The Ecologist magazine, half of privately owned woodland is barred to the public.

It gets worse still. The Forestry Commission works very hard to make our woods accessible to everyone. It builds car parks, bike tracks, visitor centres, picnic areas. When the land is privatised, most of that will go. They can put a massive fence around the forest, they just can't put up a sign that says "keep out". Look at what happened to Riggs Woods in the Lake District, sold a few months ago. The car park has been shut down, the picnic area has been dismantled, the visitors' centre closed, and all you see when you go there now is a large, bolted gate that, legally, you are allowed to clamber over. And for what? To preserve our forests costs just 30p per taxpayer a year. Selling them off for ever will raise just half of the sum that one corporation – Vodafone – did not have to pay after the Tories came to power out of what Private Eye estimated was its total tax liability. (Vodafone denies this figure). So if you go down to the woods today, you'll find the best metaphor for Cameronism. Change your party's logo to a lovely green tree – then sell off all the real trees to corporations. Oh, and then say you are "empowering volunteers" by doing it.

The Prime Minister has said the forest sell-off "empowers local communities" to take over the forests for themselves as part of a "Big Society". Yet sources within the Department for the Environment, Food and Rural Affairs say that, unsurprisingly, only about 1 per cent of the sales are anticipated to go to local co-operatives or green groups. The "Big Society" is a fluffy fig leaf for dismantling and demolition.

But, amazingly, this may not be the biggest environmental vandalism of the Cameron years. The Conservatives have just authorised the launching of deep-water drilling off the coast of Shetland. The White House investigations are only now uncovering quite how disastrous this tactic was in the Gulf of Mexico – but it would be worse in the Shetlands, where the very harsh, cold and windy conditions would make a clean-up dramatically harder and more expensive. It would have to be bigger too: Chevron has admitted that if things went wrong it would release 77,000 barrels of oil a day – 25 per cent more than went into the Gulf.

The Health and Safety Executive warned that serious accidents on British oil rigs almost doubled last year. These are the very warning signs that preceded the Deepwater Horizon catastrophe. Even if the oil is excavated "safely", it will then release huge amounts of carbon into the atmosphere and destabilise our climate even more, which doesn't sound very safe to me. As if that wasn't enough, Cameron has also authorised drilling for shale gas off the coast at Blackpool – an extremely controversial practice that is suspected by many scientists of poisoning water supplies at several sites in the US.

Britain's forests and seas do not belong to David Cameron. They belong to us. As Bill Hobman, the former chairman of Forest of Dean District Council, says: "Mr Cameron should show us the deeds to the forest. How can they sell something they don't own?... This is a wonderful part of the world and shouldn't be auctioned off to the highest bidder to have their own little bit of heaven. We will fight this all the way." The fightback will be ferocious, and, like the inspiring fight against super-rich tax-dodgers, it unites people from the Tory shires with amazing left-wing activist groups like 38 Degrees.

This is a fight about what we value as a country. Do we want to preserve Britain's most beautiful places – forests and seas that were alive for our distant ancestors, and should be alive for our distant descendants – or do we want a few rich corporations to make a little bit more money from destroying them? David Cameron has made his choice. Now we need to make ours.

You can sign the petition to save our forests: click here.