Sorry I did miss that I was thinking of partition walls. You are not allowed to run cables within the cavity of walls, so you will need to chase out, you are also not allowed to chase more than one third of depth of wall so to chase out 50mm the wall should be at least 150mm deep/wide/thick.
You can use permitted zones as mentioned in OSG relating to the cable route taken from accessories.
I'd recommend that the circuit was RCD/RCBO protected at CU.
But your electrician will know all about that? If the circuit is not already protected by rcd, it will be likely that it is not considered minor work as protective devices will need to be replaced at CU. So will then be considered a new circuit and will need to be notified if work not carried out by registered electrician. This circuit will need to be inspected and tested to assure it complies to BS7671:2008 so certs can be issued.
Is that the point you was wanting me to make?
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