whats involved swapping single indoor socket to double on block wall?

[bricol]

I've always just taken my bolster chisel, cut the plaster as required with it . . then wellied the required hole out in the wall behind it. Slight hint of filling around the box needed.

I did use an SDS drill on rota-stop for sockets that were in a room that was an extension - so one wall was flippin' hard brick!

 

[roofman]

if the need for a double is overriding then just fit a double wall mount over the top and even put another next to it so you have 4 sockets

 

[roofman]

just fit a couple of wall mounts spurd off the single...4 sockets in one hit