No policy or contract of bodily injury liability insurance which contains any representation by an insurer to pay medical expenses incurred for bodily injuries caused by an accident to the insured or any relative or any other person coming under the provisions of the policy, shall be issued or delivered by any insurer licensed in this Commonwealth upon any motor vehicle then principally garaged or principally used in this Commonwealth, if the policy contains any provision reducing the amount of damages covered under the liability or uninsured motorist coverages of the policy by the amount of payments made by the insurer under the medical expense or other medical payments coverage of the policy.