Funny how many of the rules no longer apply when they are too expensive to be convenient.
The units doing it have a dispensation from the CAA to trial it. I guess with a view that the rules will be changed in due course. It is subject to risk assesments and strict procedures and training. And its been common practice in other European countries for some years.
Also, it was the UK's largest ANSP that drove this change with the CAA.