I think he's being mean. If he’s got to plaster the whole wall anyway, it’s really nothing for him to dob a bit of extra plaster in that setback. Doesn’t even have to be neat, just roughly to fill the gap. If you’re doing it yourself and you’re not that good at plastering, batten the wall out to the level of the new bricks, put some bonding/browning/render on it and use a piece of timber to drag it level across the battens using those as your marker. When it’s gone off, remove the battens and fill the gaps where the battens were. It’ll then be good enough for him to skim over. £400? He’s having a laugh.
