The screws that hold that facing on are generally pretty small, they are only around 6mm long, I've tried sourcing longer ones as most new builds have this but failed twice after they were delivered and didn't fitso gave up. When i've done it i've had to loosen off the socket that is behind that and actually has the switches mounted into the actual socket backbox to bring it all forward and screw the facing on with a bit of fiddling around. It is a pain but can be done as widler said, i done two last week and didn't leave it like that
I've done loads of them, and they should be left like this...
Take the face plate off, loosen the back socket, cut your tile leaving small tabs to go in between the screws to keep the back plate flush with the tile then screw the face plate back on..