The court heard that C [...] wanted to experience sex - and so he had asked his carers if they could find him a sex worker
Given C has the money to spend, and is able to communicate his desires to his carers, why can't he communicate with escorts directly and find one himself? Apparently he has been judged to indeed have the mental capacity to consent. But he doesn't have the capacity, somehow, to procure SW services? Is he deprived of the freedom to use the internet? I'd say that's even worse than being deprived of sex.
Maybe he can't read due to intellectual disabilities? Difficult issue. In C's case, seems there are behavioural concerns:
The characteristics of C raised a serious question about whether it would be appropriate to expose a sex worker to the risks of spending time alone with him.
For the sake of safety for all involved, how about group sex then? Or a volunteer, friend, or carer, and an associate of the WG could simply be present for the proceedings. I realise this would make the booking more expensive.