The ring final is the odd one out, near every other circuit is protected at the origin and what ever you do you can't over load it without a protective device disconnecting the supply, there is a 3 meter allowance between to origin and where the protective device is placed, but your not allowed any branches so can't over load it.
However with a ring final taking power too need the consumer unit can over load it, and also unfused spurs can have one double socket so two fuses in the plugs so you could over load an unfused spur.
One would hope the supply to the shed if taken from a ring final is reasonable central on the ring, and it has a FCU or 13A plug at the origin, in which case having a switched FCU as the light switch as well as the double socket is OK. However if there is not a single fuse protecting the supply to the shed, if it were taken as an unfused spur then you would need to turn the socket into a fuse and socket possibly also with a switch so a single 13A fuse protects all. This stops you exceeding the permitted load for an unfused spur.
If the supply is taken direct from the CU then there should be no problem, it is only if taken from the ring final, as since it is very unlikely you will draw 22 amps from the shed supply it is not really a problem, it is just not complying with rules. If one considers a shed is likely to have over a 2kW load appendix 12 suggests it should have a dedicated supply.
So since you don't say where the shed gets it's supply from we can't give a 100% answer, all we can say it is likely OK, but we can't be sure.
