Thanks for the feedback guys. Much appreciated.
Here's some more info just to put a couple of minds at rest. The cable which currently runs to the workshop was for the old shed the previous owner had. The cable itself is up to scratch, what isn't is the power source, which is a socket in the conservatory. I plan to get a sparky in to join the circuit with the one which currently goes to the garage, or however he would recommend it. The wiring inside the shed I will do myself.
In the workshop itself, I plan to have 3 or more lighting points which will use low wattage LED lamps. I will have up to 4 double sockets in there too, more for convenience than any industrial level machinery. At most I plan to have a chop saw and router otherwise the power will be for a spot light and any lighter hand power tools I may need, there will be no instance in which more than one tool is active.
AJB, that would be nice if you could PM his details. Thanks a lot. I'm between Sittingbourne and Faversham which is a right faff to get to from your neck of the woods, so it depends where he's based more than anything I suppose - but would be good to get someone who I can trust to know his stuff.