An article in the press yesterday said that the Bank of England's interest rate would stay fairly flat for about five years so I don't know what would happen to your mortgage rate over that period time. It partly depends how much you owe on your mortgage and your attitude to debt. Personally I hate debt of any kind because it makes me indebted to somebody else who can control my fate, so I'd probably use the money to reduce my mortgage, even if saving it made more sense financially. From a financial viewpoint it's normally advised to save the money if the savings interest rate is higher than your mortgage interest rate, and repay the mortgage if that interest rate is higher than any savings rate you can get.