There is no definitive 'answer' to your issue, but you've been given a number of very sensible options by people who very much know what they're talking about.
It sounds rather like you already had an 'answer' in mind before you asked, and it isn't one of the suggested ones?
I think the trouble is you've forgotten what my question was, as I didn't ask for "options" in the OP.
I did ask for someone to check my shopping list to install both a master socket and an extension, that is all, nothing more.
Which means details on the existing master socket are totally irrelevant.
Which means an unrelated 9 year old thread is irrelevant.
Which means talk of junction boxes is irrelevant.
It sounds rather that too many posters are answering questions they have in their mind rather than the questions asked in the OP.