* It's shed wiring. Pulling 3kW through existing rings(?) in sheds
that were wired who-knows-when out of who-knows-what has often been a
problem.

House CU with dedicated 40A RCD to shed -- buried 15 metre 40A
armoured cable spur -- CU in the shed with 30A RCD socket ring and
10A RCD lighting ring. Put in on 31st December 2004.

I'll put in a new breaker. What is an "interlocking" socket?

I can't find a suitable downward-pointing, switched socket anywhere.
Can anyone help?

Thanks for all your help