OK, thanks all for your highly valued opinions... this image is obviously a polariser, which I guess is a good thing. Wouldn't it be a boring world if everyone agreed about everything?
Anyway, I attach the final version, which I am not going to change no matter what anyone says: foreground cropped as per Mike's suggestion, aspect ratio now A3, a tiny bit more detail in what was the resolutely black cloud, but otherwise not much changed from the Van-Halen-meets-Turner-In-Africa original. Which is what I saw, even if it wasn't there.
Ed: It's what you want, and that makes it perfect.