I must admit I have never been to Cornwall Ian, and the last time I was at the South Coast was a lifetime ago in the early 60s when I did my training as a young Marine and I still recall how cold the water was more than forty years later.
The season doesn't really bother me (in the UK its never that cold in the winter or that hot in the summer either)
I am rather partial to photography in the winter - there are far fewer people out and about to detract from my landscapes.
Fog can usefully isolate stuff from a distracting background.
Rain brings rock surfaces to life.
What bothers me is the grey overcast skies that last for days on end giving a very boring flat light - we seem to get them a lot in both mid winter and mid-summer.
To me the best light occurs when rain (or occasionally) snow storms are about to descend - the camera and I end up getting very wet - but if I have at least one decent shot in the bag, I can go home happy to dry my kit out.