Under UK law, it's not an approved instrument approach procedure. So you aren't flying an "approach", you're just flying under IFR and trying to descend below cloud to become VMC to fly a visual approach. So comply with all the IFR rules, just as if you were enroute.
If you can't descend to VMC, go to somewhere that you can (ie somewhere with a proper IAP), descend below cloud there, then fly VFR to your destination.
If you're under the hood in good VMC with an instructor, there's no reason at all not to "practice" IFR approaches with that spoof procedure, just to learn how to do it. But don't do it "in anger".
One day, the UK may go to the US system whereby you can fly an IAP with no App/Twr (indeed, with no ground-based radio at all). Could work in low-traffic-density areas, I suppose. Don't hold your breath...