The "Review of British Mammals" 1995 by Stephen Harris et al (the link below should take you to it)
A review of British mammals
opulation estimates and conservation status of British mammals other than cetaceans
reckons that there were only about 200 - 300 in the UK outside of the populations on the Shiants (and possibly still Lundy), the only records were from port areas, so that makes it a fairly tough call I think.