Well, Kensington and Chelsea still has steady , if not, rising prices. There is such a shortage of houses on the market that it isn't going to get better. Flats are selling much higher than last year. Even if it were to drop it would have to by a huge percentage to get to a 'reasonable' level, whatever that is in such a booming city.
For Russian, Middle Eastern and asian investors there is no comparable city to London. New York is not exactly as friendly out of 2 of those 3 groups. The rest of the cities in Europe do not hold a candle to London.
Granted Brent, Tottenham etc may see price declines but not the prime areas. Even if they decline it wont be by much. Globalisation at work.
Make the money elsewhere and live where its nice.