Socket Spur

Hey Guys
I have just spurred off one socket so that I could install another. I have fitted the box flush to the wall and wired up the socket and all seems fine.
I have become stuck as I have my cable running down the wall until it goes under the floorboards.
My question is......
With the cable that is coming from the socket to the floor. Do I need to drill out the brick underneath the socket to fit the cable inside or can it be just be placed behind the plasterboard when gets boarded????.
This is for a living room in my house
I hope my question is quiet clear haha.

Behind the board should be fine.

Some other things to think about though:

RCD protection?
Is your new socket correctly spurred?
Did you test it?
And is Part P relevant?

Well I've ended up hammer drilling a line down the brick where the cable and fit nicely.
The Socket is correctly spurred and is RCD protected.
Havent tested it as of yet as waiting for my friend to borrow me his tester. But the socket itself will not be used until tested so all seems fine .
Thanks for the help