The 20% scheme would work as a gov. loan. They won't meet the repayments and will start to falter gradually beyond the next election, the housing market will be propped up (if anything rising again) so that the owners will sell down and the government will get their money back. Giving them 6 months to a year to think things over on a trade down from their beloved house, gives them time to get over it. It won't be seen a soft touch socialist measure if it is made clear that it is a special one off. Along with the regulation changes chaos is staved off. All over by mid-term next administration.
Remember the Saving and Loans crisis or the Asian Contagion ten years ago? It's not the end of the world, just a correction. The government in a civilized society upholds decent behaviour between us so we can trade freely as possible. They screwed up on their watch, it is the least they can do to compensate in the most cost effective manner. It won't be seen as bailing out the reckless but a short term contract and a drink at the last chance saloon for the reckless. Meanwhile the CEO of gov. and advisors go and if there is clear evidence of reckless intent in gov. and/or banks, prosecute them for bringing the financial system into peril. Somebody's got to walk the plank - even people lying about their means when getting a mortgage. The compensation is much the same as the criminal injuries payout system. You walk down the street and if you get assaulted you get a payout from the government for failing to protect you (especially if it some known nut who escaped from Broadmoor) the assailant is banged up and made to pay you compensation too. Free market reforms have had a wonderful effect in Britain since the 1980s. It is a vibrant cosmopolitan place and still could get *a lot* better. Many own their homes, have cars, much foreign travel (it broadens the mind) and many people visit. This has happened or is happening in other European countries, Russia, China and parts of the third world. Globalisation of capital has been a good thing. I'm just old enough to remember my mother having to wait 9 months to get some massive, crappy, Bakelite second phone (only an extension) from the Post Office or the crappy British Leyland cars. The old guard and new feudalists want to return us to, dare I say it, state housing (one size fits all), cars as luxury items (global warming), no foreign travel (global warming), composting allotment owning vegans (methane, global warming), lights out at nine pm (global warming), isolationist, free thought limited, little surfs living short miserable lives. The system is a bit broke. Well we fix it. It's not the end of the world. Be rational.