At present I am building an extension, with the new extension placing the external electric mains that is connected to the sofit board on the inside of the extension, does this have to be re-routed around the extension or can it be boxed in (appropriately)
from mention of soffit take it it's an O/Hd supply.
if 2 single cables spaced apart then prob needs moving as even if insulated (which many aren't) not good to touch/box.
if single concentric which looks like SWA then may be ok to box if its after cable fixing point on house so no chance of it fretting due to wind movement.
Difficult to say without seeing or more info