I would suggest two options.(posted 7665 days ago)Either there was no MIG purchased - claim fraud/negligence as TSB took the money and did not do what they undertook to do or There was an MIG but TSB could not claim as the had lost the remaining documents to support the claim - again claim negligence. Of course you have the issue of subrogation - however as the MIG was blatantly mis-sold in this case you need to add this to your defence.
I would suggest a counterclaim for the proceeds of the policy and/or the premium.