IMO, it's not as simple as b789 suggests.
MET manage the site and were clearly nonplussed by the quoted POPLA decision. But they have a contract and IMO won't surrender all income easily.
Previously, the assessor stated that they had allowed the appeal in question because MET had failed to rebut the appellant's claim that the land was not relevant land.
But now they are and their evidence makes their argument clear in that there is NO statutory provision which 'imposes a liability (whether criminal or civil, and whether in the form of a fee or charge or a penalty of any kind) in respect of the parking on that land of vehicles generally or of vehicles of a description that includes the vehicle in question.' Therefore although subject to the byelaws, it is 'relevant land'.
I suggest the OP deals with this argument in detail rather than generalities.
The creditor claims and states that there were numerous and clear signs setting out the terms of parking.
The landowner is the 'Airport Company'.
Byelaw 3(28) states that 'no person shall..fail to comply with a ..sign exhibited by or on behalf of the Airport Company?
Byelaw 2 deals with Penalties and byelaw 2(3) states that the penalty for contravention..of any other byelaw shall not exceed level 3 on the standard scale.
It seems quite clear that the creditor's evidence is seeking to disapply the byelaws in favour of their contract with Starbucks, the lessee. (OP, I haven't seen the landowner authority. Is it Starbucks and are they a lessee? I'm assuming they are.)
That the land is not 'relevant land' cannot be disputed as the byelaws are clear, and this is a matter for the assessor.
MET's attempt to disapply the byelaws is a different matter which the appellant will address with the Airport Company direct.
My thoughts.