There is a slight problem: if overlay approaches were authorised in the UK (which would be great but is highly unlikely) then many IFR approved GPS installations would not be able to use them. My KLN94 uses a version of the Jepp database on which many tracks are missing, and often only the final approach track is shown.
One can still fly the published approach with it of course (it's hardly rocket science) but one would not be getting continuous course guidance in the NAV mode.