I think in East Dulwich it would be more like £650k+

A correction in overall prices doesn't mean that everything should drop so that they become the correct value. Underpriced areas should rise, and overpriced areas should fall. New transport infrastructure is one of the biggest reasons why an area becomes a 'hotspot', and people who can't afford to buy in East Dulwich or other areas on the East London line broaden their search and come across places like HOP with great period housing stock at affordable prices. Forest Hill and HOP now have much better transport links than ED, they are just missing the bars, and fancy shops which will surely come in time once the demand is there from the influx of new residents.