Never even heard of the OFCOM document.
However, saying that it stops PCL doesn't appear to stand up. CAP 168 Chapter 6 has already been cited as the reason GA can't use PCL, but the Emergency Services can.
It's been common practice for Police Air Support Units to operate PCL outside ATC hours, some at licensed airports. In order to facilitate this a discrete frequency is allocated (and kept secure) via I presume OFCOM.
Is there a general exemption ?
Sir George Cayley