Last week our buyers pulled out as their bank told them that our house is unmortgageable. We've live here for five years and are currently paying a mortgage on it 
So the reason that it is unmortgageable is that it's a Victorian semi and there's no firewall between the houses. Thinking back over our previous houses, none of them have had firewalls - including a Victorian terrace where you could have gone from one end to the other.
I know we should have one; when we had some building work done after moving in we asked the builder and he refused the work - he's only ever put them in when doing loft conversions.
I've dealt with the loss of our dream (detached!) house, but does this mean that the bank is declaring every house in the country with no firewall unmortgageable? That's a heck of a lot of houses.