London certainly has it's share of dreariness. I see so many photos hanging out front of estate offices and (for the most part), the sky is in a sunny, yet very blue way. Certainly that is not usually the case and most photographers like ourselves have spent plenty of time replacing those gray London skies with a bright, paradise-like sky.
Naturally, it would be great for every day to look like this shot below, where the sky was not replaced in this shot, but sometimes you've only got one shot at shooting a property and if you can't make it - fake it. But if you don't have to? Mate, that's like winning the lotto.