The BPA/IPC Private Parking Single Code of Practice (PPSCoP) section 3.4 states:
Material changes – notices
Where there is any material change to any pre-existing terms and conditions that would not be immediately apparent to a driver entering controlled land that is or has been open for public parking, the parking operator must place additional (temporary) notices at the site entrance for a period of not less than 4 months from the date of the change making it clear that new terms and conditions/charges apply, such that regular visitors who might be familiar with the old terms do not inadvertently incur parking charges.
So, have G24 complied with that? Are there additional signs notifying that there has been a material change in the parking terms & conditions?
If this is a retail park, I tis no good going to the retail shops. The Keeper needs to find out who the landowner or their agent is that manages the land. Usually, there will be some info on the advertising plinth.
However, as this is an IPC member, no appeal is going to succeed. It will only conclude after they issue a claim and it is defended. Are you willing to go all the way with this?