Local manager got back in contact with me to ask when was most suitable this week to have the master socket moved. I'm going to go back to him with either Wednesday or Friday, so I should have an update for you by the end of the week and hopefully be able to close this out!
Good news @StephanieG – master socket was moved to the living room on Wednesday! Same installer showed up and had the job done in less than 20 mins with virtually no mess and was perfectly friendly about it.
I haven't tested the internet from the new point yet as I had to leave almost immediately after he'd been, but I'll be there at some point this week to make sure it works and I'll post back here to confirm.
Thanks again for all of your help on this, it's hugely appreciated!