This is an insurance policy which is taken out by you for the benefit of your lender. The premium is a one-off fee that can cost several hundred pounds. The MIG protects your lender in the event that you default on you mortgage which leads to your home being repossessed. If when the lender sells your home to recover the loan amount owed to them and the sale price of the property doesn't cover the debt, the lender can claim against the insurance policy to recover the rest.
Most lenders require the MIG fee to cover the proportion of the mortgage that is over 75% of the value of the property. What this means is that if you need a mortgage amount of 90% of the value of a property, the MIG premium would cover that 15% difference if you default on the loan.
