Nitro23456 - The possibility of your diagram showing three earths is one which most people forget. In a majority of houses they use a metallic back box to fix sockets and light switches to solid walls (Concrete, Brick and Plaster). As the box is metallic it should be bonded with the earths and hence the 3 earth wires. A lot of electrical accessory manufacturers build their sockets so that the earthing to the box is done via the two screw fixings but this only works when the socket is on the back box. Once the socket is removed there can still be a possibility of a fault occuring between the cabling for the socket and the back box which would have no path to earth.
With regards to the Spur issue the 17th Edition does allow the use of spurs within a ring main. "Spur using a Fused Connection Unit (FCU) connected directly to a ring:- The number of socket outlets supplied from a fused connection unit is dependent upon the load characteristics (i.e of your circuit you propose to use this connection for) having taken diversity into account". It does not however permit you to have an FCU, radial circuit and to tap of with another FCU.
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