Is it legal to run cables through notched out joists ?
I know the preferred option is to drill holes through the joists but
in this particular case the joist have already been notched out to a
depth of 40mm. So when you add an additional 15mm for the floor board
the depth from the surface will be 55mm.

The joist are 7" deep and the notching out has been made to accomodate
a 1" gas pipe but there is plenty of room alongside for the cables.

Andy