From The Evening Standard:
The historic owner of swathes of Mayfair and Belgravia today said it had sold off hundreds of millions of pounds worth of “super prime” property in London because of fears about the capital’s overheating market...
Grosvenor’s sell-offs included 11-15 Grosvenor Crescent, which it sold in December last year for £114 million to private developer Wainbridge. The company pumped sale proceeds into rental schemes in more affordable areas of London such as Bermondsey.
Here's a chart of Nationwide's average prices in London compared to the rest of the UK (excl. Outer Metropolitan), if they published the figures for Central London it would be far more extreme:
Assuming your aim is to collect as much rent as possible and you are indifferent to absolute house prices, it would have been a good strategy to simply sell up in London and buy 'everywhere else' at the peaks and then buy back into London in the troughs. Which is presumably what these ultimate rent seekers are doing.