...and one additional qualification to the answer, which is that vis of below 10 km can be accepted on notified routes/ATZs, under:-
ANO Schedule 8.1(c)
He shall not, unless his licence includes an instrument rating (aeroplane) or an instrument meteorological conditions rating (aeroplanes), fly as pilot in command of such an aeroplane:
(i) on a flight outside controlled airspace when the flight visibility is less than 3km;
(ii) on a special VFR flight in a control zone in a flight visibility of less than 10 km except on a route or in an aerodrome traffic zone notified for the purpose of this sub-paragraph; or
(iii) out of sight of the surface.
-------
Most of this is of relatively little practical significance. For a PPL operating in the London area, one possible use for SFVR is in cutting across the north western corner of the Heathrow CTR (if you speak nicely to the controller first, of course). This could conceivably allow you to fly near Slough, if only in order to bomb it.