I have my Gr 6 piano exam in 6 days and my final piano lesson this morning.... only my voice departed last Wednesday and still hasn't come back. I am beginning to worry. I am getting better (I've had some nasty cold/ chesty bug) but can't sing above a G above middle C. I think I can probably just about make an octave down from there (only just). I know I am allowed to whistle and I think I might be able to manage test A whistling but there's no way I can whistle the sight singing..... Will the examiner be able to provide me with aural tests for such a limited range if my voice stays departed.....

I would expect that he/she could work around the limited range. For grade 7 my examiner checked my range beforehand. Some people don't have a very large range anyway!
You can also hum I think if it makes it easier.

Can't answer your question but I do hope things go well for you. try not to think about the aural whilst playing the pieces. Remember worrying will only make things worse.

Good luck

You are allowed to do the tests in any order you like, so if you think you would prefer to get them out of the way, ask to do the aural tests first. That doesn't cause any complications with a piano exam. For accompanied exams it would mean that the accompanist would have to lurk outside until it was time to play, but it would still be allowed. I certainly hope (expect is too strong!) the examiners would have singing tests for at least two different one-octave ranges. Many people who don't sing regularly have that little or less, and not always conveniently from C to C...