I think I might have some rescue remedy in the cupboard, so will try that tomorrow.
Well I built (if I may say so myself) the most amazing enclosed litter tray out of a moving box and the cat flap they have been using for a year. Showed it to them. Neither looked that impressed by my efforts, and one wee'ed on the carpet a meter away in less than an hour later.
Phoned the vets, and they think it is more likely to be behavioural as if it was medical, given its been going on for two years already, then we would be seeing other symptoms already. So she suggested multiple litter trays scattered around the house ( not very practical with a 2 & 3 year old in the house) feliway but changed her mind in that when I said we had already tried that, lots more attention to the two cats, and trying my cattery idea.
I pulled out sasha's freshly washed dressing gown out of the washing basket that I had only bought in less than 10 mins prior to pack as we were going to be out tonight, and you guessed it. Wet with wee,so that's a whole 2 loads of washing I need to redo tomorrow. Not happy.