That's not really the case. It was a widely held belief or myth that the British isles were covered in dense forest. The coverage was at most about 60% and also that humans have always been intervening in the landscape and they arrived very soon after the glaciers retreated up north. Most of the woodlands were managed or occupied and there were not many places which didn't see the human touch (in Britain) compared with other places in the world.

In part the myth of the virgin untouched forest comes from colonial views of natives existing in harmony or as part of nature and not really human. Even in the US, Native Americans have been managing the "wilderness" for thousands of years before the US Forest Service.