There have been virtually no clouds over London for the last 48 hours; is this related to the volcanic ash cloud? I seem to recall that clouds need seed particles to form and wondered if the ash had somehow 'sucked up' all the available moisture that would form clouds otherwise?
High pressure plus wind from a northerly direction means the rain has fallen in the north and clouds have petered out as they move south across the country. A quite normal happening. (BTW - Enjoy it - saw a flake or two of snow where I am. Brrr!).