Hi,
was wrong from the beginning.
they supposed to apply a bonding solution for plaster as bostic cementone plasterers stabilising primer prior to the new plaster without to remove anything.
you have few solutions but will not be cheap, as:
1) if you have normal wall boxes for your sockets or switches, replace those with slim wall boxes.
2) you can render the walls and leave 2-3 mm for plaster and re- apply the plaster after
3) the cheapest way is to design a wall face plate around the sockets and switches.