Sycamore first introduced 1500s, but only naturalised mid 1800s. How long ago were the Ice sheets? Such a long time without the sycamore making it over naturally. It being introduced not naturally arriving like the much longer species. A central, Eastern and southern European species. Typically lives 200 to 400 years, or capable of that.
One report at the time of the cutting down mentioned that it was causing damage to the archeology of the area. I do wonder if eventually it would have been cut down officially anyway.
It's been a feature on the land so long and judging by the hysteria over its chopping down it is considered culturally important. Why was it never given protected status? It is recorded as a veteran tree, lost on the ancient tree inventory on the woodland Trust site. Interestingly enough there's a lost veteran tree on the other side of the road to the gap stump. Nobody made an issue of that loss, an Ash too considering Ash die back they should keep as many of them as possible. Ash no longer reaches the sizes they used to in managed woods. Good job we're no longer using Ash for wheels and carriages so much these days.