Hotel Mama and others, the "truth" is very simple. The VHF a/g frequencies are allocated (by whoever allocates the electromagnetic spectrum, ie not the CAA) for voice comms only. PCL is signalling which (surprise!) is a different classification to voice, ergo; illegal.
If that were true, would it not make the 'speechless code' illegal also? (you know, 1 click=yes, 2 clicks=no, 3 clicks=say again etc. for use in case of microphone failure). Red herring I think. It's just the CAA doesn't want to allow it.