Currently the government owns the land which means we own the land, as everything the government owns is paid for out of our taxes. In other words they are selling off something you own without consulting you, and those of us who are saying 'no' are being ignored.
The private owners can then fence off land to stop public access to it, land that we and our ancestors have had access to for thousands of years. The Crow Law means that we can 'gain access' to this land and they cannot do us for trespass, but they can make it as difficult as possible and can prosecute you for damage to their property if you damage the fence while climbing over it.
Eventually the owners will want some kind of recompense for their investment, which means gaining planning permission then selling it to developers for a profit. if they did that tomorrow their would be national outrage (one hopes!) but if they do it in ten years time, for just a small part of that land, then again ten years after, for another small part...
This of course, doesn't take into account what hippies like myself call 'inherent value', which basically means the land exists for itself, as do we all, whatever species, not for our usefulness to others or the capitalist machine. If the land belongs to the government it belongs to everyone, thus it belongs to no-one, it belongs to itself, and that is as it should be.
The Woodland Trust has already stated that it cannot afford to buy enough woodland to make any difference, so the National Trust are probably in the same position. Also, the woodland will be sold in auction, so well meaning trusts and individuals will be priced out by rich developers. Even if we had the cash we could still be out-bid.
"The timeless giver of all life,
Offered as a sacrifice,
The priceless finds it's price,
In the greed of man"