Over the last few years, there have been several similar occurances, where aircraft belonging to schools or clubs have been used for illicit purposes.
Apparantly the smugglers are aware that Customs & Excise can confiscate any vehicle or AIRCRAFT, in which smuggled goods, drugs etc, have been found.
The smugglers obviously don't want to lose thier own vehicle or aircraft, so only used hired ones.
As in this recent case at Newcastle, Customs do seem to restore the A/c to its rightful owner, so long as that owner can prove that he knew nothing about the illegal activities, & assists Customs by giving any info that he has on the smugglers.