If you claim those air experience passenger hours as flight under instruction, beware that you could then be falsifying your PPL application.
An offence which, on conviction, could lead to a £2000 fine and/or 2 years' imprisonment. It is hardly something to take lightly. And it's clearly stated on the PPL application form.
If the pilot wasn't a RAF QFI or a civil FI at a Registered Facility, those hours of yours were passenger hours!