www.bbc.co.uk/news/uk-35140756
...
... so I can well~believe the temperature you've quoted for the Derby area, Michael.
Roughly the same up here.
But the notion of a swim ANYWHERE in in December?
Brr ... ! Nooo thanks!
Having said that, I spent a couple of hours in the sea on Christmas Day, 2008.
Mind you, that was at Myrna's relatives' beach resort in the Phils!