Your MIG (Mortgage Indemnity Guarantee) does not mean that you are let off any shortfall. The shortfall is met by the insurers under the MIG who can then chase you.(posted 8069 days ago)Your choice is as follows:-
1. Respond to the letter telling them your circumstances and your new address. Let them take what action they see fit which might include making you bankrupt. The six years during which time they must sue you starts from when you respond. They might leave it for a few years and then come back to you in the hope your status has changed - if you again respond, the six years starts again.
2. Lie low - avoid contacting them for six whole years and you are free of the debt as it is statute barred - do not acknowledge the debt at all. Bear in mind however that if they do manage to confront you, interest will have risen and the debt may after say 5 years of no contact, have risen quite dramatically.
It is up to you to make an informed choice!
I wish you well with whichever choice it is.