Doesn't the CAA have a database of all aircraft over 2000kg that ever fly IFR? They should have, since they invoice them for en route charges.
It's easy enough to discover/contact the owner of an N-reg plane. You write to the trust company. They will pass on the communication, and all those I have spoken to will reveal his identity anyway to anyone in authority (e.g. the CAA, or to some airport claiming unpaid parking charges). Then the trust company bills the beneficial owner a nice amount of dealing with the correspondence
