I'm going to be adding extra sockets to a ring which is going to be checked by building control. the house is over 100 years old and how probably been rewired many times and all the cable under the floorboards runs through notched out joists and not through drilled holes as per current regulations. Would i be able to use these notches for my new cable?? Also do i have to put the new sockets at 450mm as per regulations when all the others in the room are just above the skirting boards?
you may reuse notched joists but should use protector plates sold for the pupose to prevent nail penetration, most electrical wholesalers stock them.
You may keep to original heights but 'no worse than before' even for a full rewire, part 'M' is not retrospective, only applies to new build.