Thanks so much for all the help, comments and advice. The consensus seems to be that it is pretty poor work, but just about acceptable for the most part. At least that confirms my opinion that they should have taken a lot more care, but I will accept that the old plaster makes it look a lot worse than it is.
To answer some of the queries, it was a team of 4 guys with the oldest in his early 30s. There was a trainee, who was useless, so he may well have been responsible for much of the poor work. That's just down to poor training or poor supervision.
I haven't tried to knock any money off for the poor quality of the work, I just have to chalk that up to experience and hire someone better next time. I have paid the bill with a deduction for work that I will have to pay someone else to fix - which includes moving one poorly sited socket, replacing and wiring the BT sockets which were removed, and for fixing a cover and ducting to the extractor (although the great tips for doing this from inside may lead me to have a look at this myself, thanks). I did make clear that if the cost of remedial work was less than the deduction, I would forward the balance. I do understand that it is usual to allow someone back to fix these sort of issues, but our relationship has totally broken down and I cannot allow him back at this point. I have paid 90% of the bill at this point, which I think is fair.
We moved out for a week for the re-wiring, but we had to move back before the plasterers arrived, which is why the 2nd fix was done (the sockets and switches were loosely fitted), to help us out. The electricians had 6 working days without anyone in their way, so I don't think we have delayed or inconvenienced them in any way. That has revealed two light switches with loose wiring though, which is not reassuring.
Regarding the line of sockets, I would firstly expect them to actually line up. Also, where more than one socket is fitted, I would expect is a gap between the sockets, they don't just rest against each other like that. I know it may seem like a minor detail, but these are the little things that make the difference. I don't know if there is an 'accepted' way to do it, but that's how I would do it myself, and how it looks whenever I go into a new show home. Maybe it is easy to do in plasterboard, and impossible with old plaster.
I do not have any paperwork at all though at this point, please can someone let me know if there is any documentation relating to part P notification or anything else which I should have now (or which perhaps might be forwarded later from a NICEIC or someone). Thanks.