The CAA has no control over the use of radio at unlicensed airfields - that's a matter for Ofcom.....
Not true, I'm afraid. Take a look at ANO Article 205/206 and the radio station licensing procedures applied by the Directorate of Airspace Policy.
And CAP 168 is a document published by the CAA setting out rules and so on in order to implement its obligations and policies. To that end, CAP 168 Chapter 6 para 11.1.3 (and many other references) are there because the CAA wants them to be there.