If it is the same property it makes me wonder why he didn't do all the work at the same time. I am not qualified but have replaced ring main sockets and light switches. There is no time involved just replacing like for like but channelling out and re- wiring and making good would take up labour time.
6 sockets and two light switches wouldn't cost more than about £30 I would suspect. A plumber I have used quite a lot in the past just charged me £65 to tighten down the gland nuts on a seeping radiator valve. He will be coming back to replace the valves next week and no doubt will want to charge me for the two new valves (fair enough) and £130 ?? labour maybe. This will be the last job he gets from me. :-(