UK 13 Amp Sockets
Hi,
The cheaper (still perfectly legal and safe) 13 amp sockets do indeed open a shutter to accept the live and neutral pins, as the oversized earthing pin is inserted.
However, you photo depicts the "MK" brand of socket. They are generally regarded as the "Rolls Royce" of electrical accessories. Their socket does not rely upon the insertion of the earth-pin to open the shutter. Instead, equal-balanced pressure from the live and neutral pins, swivels the shutter out of the way.
They seem to be the only ones to have this feature, so I presume its patented by them.
Ring-circuit mains in the UK, is basically to ensure that a particular socket and its wiring cannot become overloaded, thus avoiding fire-risk.