Is the second cable from the outside socket to the shed also 4mm SWA?
Are there any extraneous parts in the shed?
Thanks for all your replies, really appreciate it. Yeah, the full run from the garage to the socket and from the socket to where the office is being built is all 4mm SWA. The shed is no longer there the cable in the picture is where it currently surfaces and if sufficient is what I hope will be connected into the office.