'After-the-event checking' of work undertaken by a non-electrician stranger does not qualify as any degree of 'supervision' in my book, so I would not expect (m)any 'registered electricians' to be prepared to certify work as 'their own' on such a basis.
Well they are the ones we hear about here - you know, the ones who are happy for the customer to buy materials, who have told the customer what to do but now they can't quite remember so could we help them because the electrician is on holiday/in hospital/uncontactable for a while/they don't like to bother him/etc/etc/etc. ... And who, apparently,
have agreed to turn up after the event, after the work has been done without notification and then after as much checking as they feel necessary in order to be happy to certify the work as if they had done all of it themselves, do tell Building Control that they
have done it themselves.