The police do use the normal airband, it is 'secret' at my local field in that it is not published, but your normal Com box will activate it if keyed on the right frequency.
And I think it is also clear that the CAA have no wish for this to become commonplace for whatever reason so there is no incentive for them to relax their stance. It just ain't going to happen here.
Quite probably true. However, must of us wonder Why CAA/OFCOM choose to regulate against this capability (as well as several other modern technologies), which have decades of proven implementation in other countries, improve utility and likely have a positive safety advantage (more common night flight, thus higher currency, more diversion airfields, etc.).
It is just another one of those annoying features where our safety regulator chooses to restrict utility for no benefit (other than jobs for the boys turning lights on after hours).
PS
Your logic also seems to imply that the double click acknowledgement on short final and the speechless code are also not authorised as they are neither voice coms nor ACARS and in fact are very similar to signaling