You've obviously never been to Beckton; it is built, quite literally, around the largest sewage works in London. On a warm day such as one that might occur in, hmm let's say July, you can literally smell the waste of 10 million people and has to be smelled to be believed.
Your general observations on the smell of London are correct. It's the stench of 2000 years!
Aylesbury is a nice town. What's going down there?