i have a fully comp insurance policy which enables me to drive vehicles not owned by me with third party cover, but does the owner of the other vehicle have to it insured themselves for my insurance to cover me.
Yes, the owner of the vehicle must have it insured for it to be legally on the road - regardless of your entitlement to drive under under the extended 3rd party cover of your own policy. It must appear on the Motor Insurance Database, check here;