There are two issues at play here.
First there is the grading of debt. A lot of people have mortgages, investment properties, CC, car loans, etc. When things get tough, it is sensible to rank these debts in terms of importance AND urgency. Mortgage might be the most important but it is not the most urgent - as said above missing 3 months payments is not going to be terminal.
The second issue is how to deal with investment property - specifically BTL - loans that have gone south. In my own case it is an apartment that is unsellable at any price and likely to remain so. The gross rent covers about 90% of the mortgage interest. Take off NPPR, voids, household charge, maintenance fee, tax and it is costing me about 3-4K pa. As someone said above, if this was a business you'd shut it down - but you can't. And like any business, conditions have changed, assumptions that were made 5 years ago no longer hold. There is no way I can afford to pay off capital now or in the future. So what to do? Morally and legally I accept that I am liable for the debt but I have to put my own and families interests first. I know that as long as I keep paying the bank interest, they will be 'happy'. I also know that it doesn't solve the problem.
I also know that the bank are scared witless that me and countless like me will just say 'To hell with it' at some stage and default. The bank will then repossess the property, realise that it is unsellable (ironically because their mortgage department won't give mortgages on apartments outside the main urban centres) and then they have to come after me. They may or may not be able to get me to sell my PPR - but that is in NE too - so no solution there. Once they have a judgement on my PPR, i'll stop paying that mortgage too. The nett effect is that the bank know only too well that defaulting is contagious and solves no problem.
What are the banks hoping for? 3 things, as far as I can see. First, is government help to stabilise their balance sheets - this has largely been done. Next, they absolutely do NOT want the proposed insolvency legislation - as that makes defaulting at least more attractive. Finally, the only long term solution for the banks is long-term inflation reducing the debt effect.
Make no mistake about it, when the day comes that you have a penny of nett positive worth, the banks will swoop and take all you have if you have defaulted. They're just waiting, knowing that the government will keep bailing them out. They're is no long term risk for the banks.
For the mortgage holder, in the present legislative environment, there is no benefit to defaulting. The banks WILL NOT cut a deal. They will just wait...and wait. The only risk for then is the new insolvency legislation which completely scuppers their wait and see 'strategy'.
As an individual, you can forget about the moral hazard and 'greater good' argument. You have a loyalty to yourself and family, period. Whatever course is best for you, do it. Unfortunately, without cash or assets, you're only codding yourself that there is anything you can do.