'Yes, it's horrible ... everyone at work is talking about it'

Theories as to its source have ranged from animal urine to a major breakdown of London's sewer systems. One London teacher said on a discussion board: "Yes, it smells horribly this morning - all the teachers I work with are talking about it.

"Only thing I can think of is a sewer main broke or something? It does smell specifically of dog poo but I don't know of any canine who could spread his stench this far and wide!"

Callers to Nick Ferrari's show on LBC Radio also debated what the smell could be. Jim Robins from Wandsworth said: "I left home this morning in Battersea and I thought I'd trod in some dog poo.

"I thought it was low cloud cover or pollen and then someone said to me that it sounds like a chemical spillage, but I said that it couldn't cover that wide an area."

Sean Napier from East Dulwich said "I used to live in Cape Town and we used to have this waft come over every once in a while from the sewage works but it's not as bad as that. I don't know what it is.

"I'm not sure if it is sewage, it would be a stronger smell, I would have thought. It smells more like manure to me."

Emma Jackson from Golders Green told LBC: "I'm on the borders of Golders Green and Hampstead and we got blown back by it when we opened the door this morning. I'm no country girl but it just smells very, very like manure, It's foul. It is really foul."

Javed Hussain from Twickenham added: "I just walked out my front door and the whole place stinks. My next door neighbours, they have some cats and I thought they have come and done a little bit of poo all around my garden. Pretty big stuff because it really stank."

One blogger, called Jim, said: "I live in south London and it stinks. It smells most like pig muck from fields, but I am 10 miles from the nearest farm at least."

Another, whose initials are JS, added: "Pretty much my entire office has smelt it and they all live at different ends of London (some in Reading and Essex!). It's more than the usual stink of London."

Rob Green added: "Stank in north London, stinks in east London. There must be a flying poo monster hovering over London."