Part P/certificates on completion of job

[flameport]

Electrician himself writes up the electrical installation cert
....
Electrician goes home and sends notification to NICEIC

More likely is them doing the certificate on a computer or similar, and doing it at the same time as the part P notification.
While some may still write out certificates by hand and such things are still valid - doing so is tedious and time consuming.

very important document if I ever need to sell the house in future

Not really.

The usual deal when sale time arrives is that any document has long since been lost or destroyed, assuming it actually existed in the first place.
Then when the vendor is asked about electrical and all the other kinds of works that may have been done in the last decade or three, the answers are: don't know, lost, never had it, can't remember, no idea, caveat emptor. Just as it has been for centuries.

 

[ban-all-sheds]

Then when the vendor is asked about electrical and all the other kinds of works that may have been done in the last decade or three, the answers are: don't know, lost, never had it, can't remember, no idea,

Don't advise people to lie and commit fraud in connection with a multi-£100,000 transaction.