Using fixed socket as extension lead?

Hi.

I have a feeling I know the answer to this but I want to run a double socket behind my TV but the nearest socket is a spur. I know I cannot run a spur from a spur but is it permitted to use a fixed socket, embed the cable in the wall with the tail coming out into the room next to the existing socket and fix a socket to the other end?

This is a backup plan, I will be getting an electrician in to quote for some work and will be adding a new socket to the ring main plus this socket but wanted to plan an alternative if this is too expensive.

Thanks.