Hi Graham and welcome to the forums.
@widdler has just beaten me to it, I think most of this may be down to confidence and a lack of experience.
How old is he? How long have you been training him? I assume he's been going to college? What quals does he have?
1. Flying solo... I'd like someone to help me on site all the time, for those awkward cable pulling moments, or for running around and clearing up after me, but it's just not practical on every single job because of the costs. If he's young and naive, this aspect of business may not occur to him. Sure there are risks, but by being careful, following the proper safety procedures etc. you can greatly reduce the risks of electric shock. Do I worry about it? Hell yeah, but I always take my time and minimise the time the installation is live during working (i.e. it's on only for the live testing). As for cutting through pipes, you just have to try and minimise the chances of doing it, maybe he needs a few pointers on how to do that?
2. Driving... pre-requisite. He may just be inexperienced and not be keen on the traffic. Having driven round Manchester on plenty of occasions, I can't say I blame him. But avoiding it isn't going to make it any better he needs to get out there and do it more. He may just be worried about pranging your van.
3. If he's young, then this is to be expected generally as he may simply be lacking confidence. You're obviously placing a certain amount of trust in him and he may not want to let you down and/or make your company look bad. If that's the case, good on him, far better that than some gobby git who makes promises your business then has to keep.
4. Generally I would say, you're the boss, give him a kick in the pants and tell him to get on with it, but there are definitely places I wouldn't work in based on their location and/or the people. Lets put it like this, if I ever end up seeing a used needle, I'm out the door.
5. So maybe he's not confident in his ability to establish whether it would be a trip risk and/or his ability to fault find if it does become an issue?
As has been said, these could all just be confidence/experience issues. You've obviously talked to him about some of this as you seem to have a reasonable picture of what he feels, but have you had a good chat with him about it with respect to the 'whys'? If not, that would be my next step.