Did you read this in the Daily Mail, perchance, OP?
London and the south east are an unsustainable bubble. An outright crash would be bad news for a small number of people who have to sell (please note - have to, not want to) and have overstretched themselves with massive mortgages. These people might end up in negative equity - but this would be a very small proportion.
For a growing majority, a crash would be a good thing long-term. It is insane that someone in my position - early 40s, professional income (not huge but well above average) is stuck in rental accommodation - with rental prices rising too. My family and I don't want to live on Park Lane - we are being priced out of zone 6, fgs.
The massive housing bubbles promotes nothing but instability and misery for ordinary families who just want a home. It is building up huge problems for the future, as the south East to becomes a ghetto for the rich.
Get rid of the thieving, selfish, parasitical non-doms, and if it brings about a crash, so be it.