I'm not sure but I'll have a guess: around parts of south London there's a definite feel of a residential building boom. But most of the new properties are out of the range of normal people. So I guess there's just a lot of demand to be soaked up at the higher end of the market, which means the big companies will focus on putting their capital into that, particularly with limited land availability. In the long run an increase in house numbers should affect the bottom end of the market too, but at the same time the population of London is growing, so perhaps new building at the top end will have little to no effect on the bottom end.