In my garage I have a single, surface mounted double socket. I would like
to take a spur of this so I can run more stuff at once (usually a radio, and
a couple of power tools) without have to constantly plug and unplug stuff.

I know that one shouldn't take a spur of off a spur unless a 13amp fused
thingy (I can't remember the actual name for this but I believe it will
basically be a surface mounted box with a fuse) is used but is there an
idiot's way of checking whether the existing socket is on the ring or is a
spur itself?

If I do fit a spur I presume that the cable from the existing socket should
be fitted into conduit to the second socket/fuse thingy. Will bog standard
plastic conduit be okay or should I go for something a bit more industrial?

I am quite happy at wiring things up as I've replaced sockets and lights
before but I haven't tried spurs yet and I would prefer no to kill myself or
burn the house down in the attempt.

Cheers

Mark Spice