LASORS describes only two cases where PICUS may be claimed:
Case B - Co-pilot performing duties of PIC under supervision of pilot-in command
Case J - Pilot undergoing any form of flight test with a JAA or CAA authorised examiner
Case B only applies if, among other things, "the flight was conducted in an aircraft having a Certificate of Airworthiness that requires its flight crews to include not less than two pilots" and LASORS further states that Flight time as PICUS, apart from as specifically provided for under Case J above, will only be allowable for the holder of a PPL subject to the terms of a prior agreement with the CAA." so I'm afraid that shoots down Gus Honeybun's Argument #2 (better stick to birthday bunny-hops, Gus)
Since a dual check to satisfy currency requirements, syndicate rules, insurance requirements , etc. is not a flight test and, in any case, the flight is not, we assume, with a CAA or JAA authorised examiner, Case J doesn't apply and Pu/t is the only option.
Of course, you can enter the flight in your logbook as anything you like - that's up to you. The CAA, however, will not accept it as counting towards any required PIC hours for licence or rating issue and so there's not much point.