As H C Andersen has explained, if there's nothing on the tariff board about spaces reserved for permit holders, then the "
friends of Boston Manor" signs don't mean diddly squat.
The tariff board says:

You haven't done any of those things, so you cannot be required to pay a penalty charge, end of.
Arguably if someone parked in one of those bays with a "
friends of Boston Manor" permit, they could be issued a PCN because they're not displaying a valid pay and display ticket or disabled badge, which is what the tariff board requires.