When I saw OP with a couple of replies I could see where this was going and have ignored it like the proverbial hot potato. Seeing 3 pages I had a peep...
I always take comprehensive photos of any diy that I do, I hate not knowing what's out of sight. Plenty good enough for an electrician that recognises the benefits of a proportionate response, electricians with a chapter and verse chip will be weeded out by the homeowner foreman.
Actually it would fit the legal definition of fraud - making a statement known to be false for pecuniary advanatge.
If the work has now been done, and especially if now plastered over etc, then the only people that can legally regularise any requirement for notification would be the council's Building Control department. If there isn't any notifiable work then no "sign off" legally required - although you could face issues with (eg) insurance.
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