@Cybercynic - "Just the people with 5-10% deposit and those that bought recently may suffer"
Why might they suffer? The set of circumstances is actually much more restrictive even than the criteria you've described. For anyone to suffer, they need to have:
a) Bought at or near the peak, AND
b) Be heavily indebted (high LTV), AND
c) Suffer a major personal / career setback that means future income is irreversibly reduced to less than that needed to make the mortgage payments and other bills, AND
d) Have no other option but to sell during a trough
That's a pretty tough run of luck. And I've never said it can't happen - there are lots of very unlucky people out there - just visit any A&E department. But I do not accept that a tough run of luck that forces the hand of some homeowners means that every other owner will also suddenly think "One of my neighbours just sold their house for less than they paid for it ... I'd better flog mine too, and at an even bigger discount just in case there's nobody left to buy it off me next week!" In fact - I think that there'll be practically zero owners who behave that way.
On the other forum, they call this "STR" - Sell to Rent. Sort of a ballsy, gutsy 'bet the farm' minority who see themselves as demonstrating their anti-BTL, anti-HPI credentials. Not many of them did all that well financially out of their decision to sell and rent while they awaited the fabled crash they've been slavering over since that site started in 2004.