Are you aware that the Life Assurance and Critical Illness Cover (CIC) that you talk about is not PPI and as such I don't think you are able to claim these premiums back.
If you aere able to claim these premiums back then I would absolutely think twice before looking to get this refunded as this policy is what will repay your mortgage in the event that you were to die within the term of the mortgage or to suffer a serious illness within the term.
Life Assurance and CIC is unlike PPI which (if claimed on) will pay out a small cash value every month, the life and CIC policy will pay out a lump sum to you and (if the job weas done correctly) will payout a minimum value equivilant to the value of your mortgage balance (at least)
When sold against a mortgage is it pretty hard to mis-sell something that will repay the mortgage balance in the event of your death. Unlike PPI which was often sold without advice, knowledge or qualifying whether you could claim on the policy - Life and CIC policies are underwritten before they can go "On Risk" and so you will have gone through a medical questionnaire at the very least to qualify and implement such a policy.
Whether you can claim on this type of policy or not I would recommend that you do not try to claim these premiums back as it will almost certainly end up with the policy being cancelled and your mortgage having absolutely no cover to repay the balance in the event of death or serious illness. This would mean that if you have a joint applicant on the mortgage that the full debt would fall on their shoulders if you have no cover.
I would highly recommend that you speak to a mortgage broker or a financial adviser before trying to claim......it could cost you far more than lost premiums