Don't blame the electrician, when chasing walls out it can go either way depending on the wall itself, nice clean chases if the plaster is good or as with many old houses the plaster is already blown waiting to fall off the wall as soon as it touched, it's not the sparks fault it starts dropping off, i've been to jobs were i've told the customer before i started work you will need a plasterer to redo most of the wall as when you knock on the plaster it's hollow and you just know it wont be just filling a chase.
That work doesn't look like it's been done by a spark even a crap spark, more a diy warrior/landlord thinking they'll have a crack themselves and save a few quid, i'd get an electrician in who can rectify and improve whats already been done.