When I did my conservatory, I extended the ring from the back wall , as it was within the conservatory, ie the same back wall. I put had a double socket directly behind the one that was in the house, and then continued with the ring into a 5 amp fcu to feed the light.
With regards to the cabling, the fcu was mounted next to my new double socket, and I used mini trunking to go up the side wall and continued to follow along the wall , but following the angle of the conservatory roof, up towards the centre , ie it was still fixed to the wall, but all in the mini trunking. Once I reached the top of the conservatory (the wall side) , i fed the cable along and down to the centre of the room. Then back again and over to the switch (the switch 'drop'). My switch was located at the other side of the room, so again I followed the angle of the conservatory down the wall , only on the other side of the conservatory , but still on that same back wall , and then come down the vertical to my light switch.
Had I ran the cable in vertical or horizontal lines, my back wall would have looked hideous in this lovely new conservatory , and as it is now - the mini trunking blends in perfectly with the white upvc framework, so much so , that you hardly notice it!!
I assumed this would be ok, for reasons that the cabling was in mini trunking, and the mini trunking was always going to be visible and not plastered over! The house rings are all rcd protected, so obviously the conservatory wiring is also rcd protected , so if anybody was to sabotage the cable, the protection would be there.