Following up to "Keith \(Dorset\)" :


Anyway, if it were that much of a problem, how on earth do they ever manage
to grow anything further south, on the Scillies, or more southerly still in
milder regions of the continent?


It'S not the mild winter /per se/ it's an unusually mild one that's a
potential problem.
Down south the predators and prey have had (hundreds of) thousands of years
to reach a balance for the local climate. An unusual warm or a
particularly cold winter even there can have similar effects.
--
Tim C.