As a side note, the size of woodlands might not be a limiting factor per se - in Northern Germany, the species occurs in relatively small patches of forest interspersed between farmland and hedgerows, in a landscape and climate very similar to parts of England. And that's despite the co-occurrence of Beech Marten (a possible competitor with overlapping habitat preferences), Eagle Owl, and (in some parts) Wolf and/or Lynx. This seems to indicate that the decisive factors are prey availability and suitable nesting sites. Of course, road traffic is also a factor - somehow, mustelids get run over all the time.