Silly question, but have you spoke to the CAA Aircraft Registration department? In my experience, they tend to be one of the best organised and helpful departments within the organisation. Just beware that sometimes their hands are tied with regards to legally what information they're allowed to give out. Contact details on the link below:
https://www.caa.co.uk/Aircraft-regis...ice-standards/
It is my understanding that even a registered "Trustee" must have an ownership claim on an aircraft when they register it, and so unless the CAA made a mistake (or were given false documents) then at some point the "Trustees" have declared an ownership stake. This is unlike the DVLA where you are simply a "registered keeper" and so not necessarily the owner of a vehicle.