I don't know about plecs although my LFS does sell "Butterfly plecs" which they keep in their large pond outside (no idea what this species actually is but it ain't no dwarf!). Anyway, another interesting creature is a Hillstream Loach which is apparently fine outdoors in winter (the LFS is in Bedfordshire).
Whereabouts in UK do you live? Our American friends might not be aware of the vast array of climates in such a small island. If you live in the South winters are not likely to be severe, even though we are getting more snow these days. In the North, particularly in the mountainous regions, it's a rather different story.