It probably goes without saying that recumbents, and recumbent tricycles in particular, are the opposite of invisible to motorists. Not being able to see past cars is an issue when your eyeline's below window height, but one of ability to make progress rather than of safety. (You have to treat every car as if it were a van.)
Of course it's hard to convince someone of that, other than by giving them enough cumulative experience of cycling in traffic with/on one, which isn't an option if they don't have something to ride. 'Common sense' says that being seen is about optics, rather than psychology.
Perhaps one of the less low down 'bent trikes might be an option? Deltas like the Hase Kettwiesel might be less stable at speed than tadpoles, but they tend to give a higher riding position, and there's something to be said for the turning circle...
(My limited Pashley trike experience confirms mrcharly-YHT's synopsis. It's a nice machine for pootling to the shops at approximately walking speed.)
We did try to explain the psychology to Coco but she didn't get it (being overly logical) or perhaps didn't want to get it. Phillipa gets it (but then she would, she's my daughter
). She was also taken with the Kettwiesel, perhaps because it looks like a three-wheeled Dino which is the bent that she knows. If the folding version goes small enough to get through the flat and into the backyard for storage then it could be a solution. It should be born in mind that the objective is to ride where the traffic is not, not where it is so a certain part of this is a mute point.
I am aware of the behavioural changes created by changes in road camber. My other thing is driving unbraked sidecar outfits which are quite assymetric. One lives and learns with it and it's more of a problem when you know how to ride with camber one way and you discover the opposite side than if you are learning from scratch.
I remember Pashley trikes from several decades ago when there were issues with axles braking due to poor design and poor materials, which is partly why I asked the question. Weight, of any sort of option, is of course a worry.
The Mission trikes are interesting but they are a UK operation which doesn't help me. I will have to find out who handles them (or makes them) on the continent to find a dealer. I think I could be trawling some dutch web sites soon.
Thanks for your help everyone. I will probably do an update when a solution has been found.