There are 2 distinctly different things here....
1. Boating - be it in a RIB or Inflatable - is great at an time of year - and a bit of 'weather' can add some spice to it - but a day when it's like a mill pond and you can skim accross the sea without a care in the world is an experience that has little equal.
2. Diving - around the coast of the UK - in winter - is surely only for those amongst us who have serious gaps in their social lives !!
Now, diving in the Red Sea at Sharm-el-Sheikh in warm, clear waters with coral reefs and shoals of colourful marine life - that is where diving should take place.
(As I will be doing frm 14 - 20 April