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I prefer to cut it with a multitool (usually a messed up blade will do it) then chisel out. That way you don't have to worry so much about the brick dust which is one of the worse for being tiny particles. Not only does it get everywhere, it's abrasive and not good for your lungs. You're still going to get a good taste of it even chiselling. Different types of brick also make a difference to how easy they are to chisel.
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Less facetiously:
https://www.amazon.co.uk/Pattress-Wall-Socket-Template-Electric/dp/B01E1LFU1M
and a mains drill with dust extraction worls well.
If you are (ever) West
I have a plastic template you could borrow.
Also, I want to inset my plug sockets on a dividing wall. Looking online it seems an angle grinder is the best way to get into the brickwork. Anyone done this?