Thanks for your comments on this project. I didn't realise that building regs would be a requirement for this and found this out afetr I postged the message.
From what you have said It sounds a little complicated for me and wouldn't want to risk life and limb to save a few quid, so i've...
I need to run cable to a summerhouse and want to install two or three sockets.
Some time ago I had an old coal bunker converted to an office and had an electrician install the electrics.
He connected and installed a breaker box from the mains and then installed two 13 amp sockets...