There's not been 125% mortgages for a long time, (since northern rock), and given house price rises in the interim, most of those are now in positive equity, it's not bad debt if the property is worth more than the loan secured on it and the borrowers are able to pay.
Most companies who were doing big redundancies have done them, unless there's massive interest rate rises, most people can afford to pay their debts.
New mortgages are only being offered on very strict lending criteria, meaning the chances of the new people borrowing now defaulting are reduced.
We've been hearing about a house price crash coming any time soon since around 2007, apart from a brief period in 2008/9 after the financial crisis, most houses in the SE have increased in value month after month to the chagrin of the crash-believers on the internet. It won't just happen, there needs to be something external to push down prices. Lending stopping again, interest rates going up to make house buying less affordable/forcing sales, massive economic down turn leading to large numbers of the sort of people who are owners to lose their jobs, vast swaths of professional class migrants leaving the uk etc, governments are going to work very hard to stop any of these things happening.
Housing isn't like any other consumer product, you can't just do with out it, and once you've got it, most people prioritise paying housing above all other spending.