Woodlands currently occupy 12.6% of the UK land area which is almost double the urban area.
As an explanation for anyone else reading: conservation in NZ and the UK are very different. In many areas of the UK, conservation consists partly of maintaining farming practices in the manner they've been practised in these places for hundreds (sometimes tens of hundreds) of years. Which, for a New Zealander, is totally bizarre. In New Zealand, there are gigantic swathes of somewhat-pristine forest (missing mostly birds, and some insects) we can look to as a model for conservation. Farmland and conservation are pretty much mutually exclusive.
So, in the UK you might use the term wilderness for a large, very lightly farmed, very lightly populated area. Where in NZ you mightn't use the term wilderness until you'd walked for half a day from civilisation.
The cities and towns are better designed than those of new world countries which sprawl.
https://en.wikipedia.org/wiki/Green_belt_(United_Kingdom)
if anything it's too successful
I understand this is much, much less than people typically think, which isn't just an interesting fact; people base their opinions on development on the unchecked feeling that the UK is 50% concrete.