"the reported met. vis. at the airfield concerned shall be taken to be the flight vis" - MATS Part 11, Ch 2, para 4, VFR.
ATC decide if the zone is VFR or IFR dependent on met report. You decide if you want IFR or special VFR clearance.
That's something of an oversimplification, AC2. I can't quite work out the reference (is that from TC MATS Part 2, perhaps Gatwick?).
Regardless of location, for VFR flights arriving or departing, the reported met vis must be taken to be the flight vis, but that does not apply to transiting VFR flights, which determine their own flight vis.
Airfields appear to have individual SFVR weather minima for arrivals and departures, but I can't see one that has minima for transit either.
Some airfields (e.g. Luton) even have that rather stark reminder:
under no circumstances is the CTR to be declared "IMC" or "IFR".