We lived in the UK for a very long time, but somehow up till this year I never did any night time photography in London. So I don't know if summer London is always such a delight to photograph, or was it because of the Olympics. Doesn't really matter. Buildings and structures that might look dull and grey during the day, at night transform completely.
Not that the Tower Bridge looks dull during the day, but some of the office buildings an the pics below do.
The Shard is of course new and not even completed yet, but the office blocks around the Town Hall are oldish, but look good with lights on. Terrible waste of energy, but beautiful to see.
And anything with lights on will look good when reflected in the water. Plus, there is always a friendly horizontal surface to put your camera on, if you didn't bring your tripod. The only place where it didn't work was the millennium bridge, but if was because the whole structure shakes when people walk on it, so the tripod won't be of any help anyway.