Thanks for the comments.
Russ, I thought exactly as you did when I first looked at this shot. I converted it to B&W and played with it quite a lot. I managed to get more contrast in the sky, with better-defined clouds, but somehow it never looked right.
Eventually, I abandoned it altogether: I suppose I forgot that it was originally in colour.
Over three years later (it's a Christmas Day shot), I came back to it and found that a little desaturation (not much) did the trick much better than completely removing the colour. What doesn't show up well in the jpeg I posted is a rather lovely subtle pinkish tinge to the sky in the upper right, which suggests a warmth that contrasts nicely with the obvious chill.
Never throw them away!
Jeremy