Assessment is always a tricky thing. When I worked in HE we used to get industrial advisors coming in from time to time and they always wanted courses to contain more group work, arguing that most graduates would end up working in teams and they often lacked appropriate skills. However, both staff and students tend to hate assessed group work, for all the obvious reasons, and I suppose performance with an accompanist is subject to much the same problems: clearly an individual performance might be made better, or worse, by the accompanist, irrespective of the skills of the candidate.
Maizie: I agree that there is a fair range of options available - though none of them is exactly what I would choose to do given absolute carte blanche. Probably the Trinity certificates come closest because at least they let you use whichever recorder you want. I've had a quick look at LCM and though they have a good range of types of exam, all the recorder pieces in the lists are for descant or treble; you can use tenor instead of descant at the higher grades but there's no mention of other sizes.
My one area of criticism of all the boards is that they are quite rigid about accompaniment. For recorder, piano does not seem to be the ideal accompanying instrument - if nothing else, it didn't exist at the same time as the recorder (leaving out contemporary music). As people have observed here before, harpsichord or lute/guitar would be better, but I think to use one of those you would have to enter a group performance exam - a bit silly if your harpsichord player is a professional you've paid to act as accompanist. I don't particularly agree with the ban on recorded accompaniment at all but the lower grades. I can see that it's not exactly real musical interaction, but on the other hand it could be truly consistent and allow for a greater range of options.
Having said all that, exams are pretty artificial and if I do ever decide to try any, I suppose I accept that I will attempt to jump through whatever hoops are placed in front of me - it's my choice.
Does anyone know, very roughly, how popular recorder is as an examined instrument at the higher grades? I get the impression that most school children who start on recorder either switch to a different instrument or give up - neither of the schools my children went to offered recorder as an instrument. If the numbers are quite small, it's probably not financially viable for boards to introduce too many options they then have to be able to cope with.