In reply to JohnBson:
> What date would you like to go back to, the heavily polluted industrial revolution? I mean rewilding would probably be at least taking it back to the dark ages? It's surrounded by farmed countryside, it's hardly a remote area like some parts of Scotland.
Therein lies the problem!
There is no past time where the climate is as it now is, and where the influence of man on the landscape was not significant.
The point with a reservoir reclamation is that you have much more of a blank slate than elsewhere, and some semblance of control over the species.
Personally, I’d go for a forest based on our best understanding of what existed before the Bronze Age clearances, with the minimum required adaptions for climate changes, genetic drift and disease evolution required to make it viable today.