I am not a legal expert, but as far as glider towing is concerned, I believe it works as follows.
Most gliding clubs are not commercial concerns - they are members clubs which one way or another have all full members jointly owning the club's assets including the towplane(s) (usually through some form of Limited Company in which all have an equal share, or are deemed to). Their financial transactions are legally regarded as the members trading among themselves, and so are not commercial.
Tow plane pilots therefore do not need commercial licences of any sort if they are not being paid.
I should have thought that many parachute clubs operate similarly.
For a PPL to come in from outside and get accepted as a parachute drop pilot (or glider tug pilot), however, may be a different matter. A lot of gliding clubs require them to join as gliding members and to have, or acquire, some gliding experience before tugging. I don't know if parachute clubs do the same - best to ring the one you are interested in and ask them.
Chris N.