What Robin says is demonstrated in the pollen record too.
In England forests were left for hunting, but even those were heavily used. The rights to forest grazing, firewood collecting, mast fattening for pigs, and the like, were very heavily regulated.
In Scotland much of the uplands never had tree cover, and a lot more of what is now arable land was moss and bog.
Humans are the ultimate habitat creators, environment changers.
We were also the first Industrialised Nation, and natural resources like timber were heavily utilised.
The great wood of Caledon was I suppose the last great wood in the south of Scotland (north of England, maybe ? ) and we do have remnants of the Caledonian pine forests scattered about.
Rivers such as the Clyde which scours out a deep valley in it's upper reaches, has steep sided Gills running down into it that carry the feeder burns. These Gills are rich in the native tree species and the flora and insect life that accompanies that. They were too steep to be felled or grazed so were left alone. Now they are being encouraged to spread out, and they are getting a foothold along the river sides and pathways.
In my lifetime the growth of woodlands is really noticeable. I think this is due to several things. Firstly so few open fires that the pressure for collecting 'sticks' is tremendously reduced. Small scale grazing has been reduced and folks don't walk the same, so they're not collecting woods for fires either. We're all more aware of trees and there are huge efforts made to preserve and plant.
I'm not thinking of the blanket planting of Forestry Commission pine forests there, but the natural seeding and permitted growth of native trees like Birch, Oak, Rowan, Ash, etc.,
Some of the walkways, like the Clyde walkway, or the West Highland way, if joined together mean that you could probably manage to cross the country from one side to the other mostly in trees
Be fun to try ?
cheers,
M