Well said nouvapanda, I live fairly near London and I go there quite a lot. It's stupid to say that advertising at bus stops is poor because 'people who take the bus aren't going to be interested'. I go to London, I take the bus. Millions of others do the same. This is not because I don't have a car. Every day the population of London trebles when people who don't live there go there for various reasons. Most of them use public transport because it's the best way to get around in the city as cars are impractical. Plus who says people who see adverts at bus stops are taking the bus anyway? I see loads of bus stop adverts driving or walking around where I live, yet I never take the bus.
It's also absolute rubbish to say people in London are either poor or rich - that's just not the case. There is a complete spectrum and if anything more of them will be in the market for a panda than out of the city. It's marketed as a city car for God's sake!, the main market is people who want a car for shorter journeys or a second car. No, people who live in the square mile probably won't want one, but there are millions of people who live in the rest of London and the surrounding area who visit it that might.
As for no advertising anywhere else, well that does seem a little strange, but I have seen adverts in all the towns+cities near me (South Essex).
EDIT: Oops didn't realise this is an old thread, never mind.