Disconnect any dangerous wiring.. either the 6A or the 20A... then give the customer a quote for rectifying the problem..
Borrowed / Shared neutral is classed as a C2 code in industry standard guidance, i.e. see page 17 of best practice guide 4..
https://www.electricalsafetyfirst.org.uk/media/mi1oqkur/best-practice-guide-4-issue-7-1.pdf
Thus would be classed as "Unsatisfactory if you were doing an EICR...
So how can you leave it as Satisfactory if doing alterations / additions..
Unless you are also a Twat.. ??
Inform the customer that whoever wired it was an incompetent Twat as reg 314.4 has been effective since 1 July 2008... Prior to that it was reg 314-01-04
(All circuit wiring must be independent of other circuit wiring)
And you cannot issue an EIC or MWC if you have identified any defects that affect the safety of the installation..
see regulation(s) 644.1.2 since 1 Jan 2019, or 632.4 since 1 July 2008,
or 742-01-04 and /or 743-01-03 prior to that!
Guidance is pretty clear in my opinion... You either do the work correctly..
Or don't do the work, (and walk away), where you have identified potentially dangerous wiring..
Unless you make sure that your work is electrically safe, compliant with BS7671 and presents no danger to people, property or livestock!
What's the problem???
