Hi Fiona, please act on BIS's sound advice. If you have any person you don't mind hearing your personal info that you can ask, it's good to have a friend or someone sensible with you. If they can deal with starting your private recording, it will allow you to concentrate on what the assessor is saying to you.
It's no unknown for them to promise you their recording but then it's mysteriously 'lost,' 'equipment malfunctioned,' etc. So better safe than sorry.
You should tell the assessor that you have a supporter [don't mention recording] and this person can help you stay on task, remember bits if you are struggling to recall, as much as you want them to. Primarily it is your job to answer, but I think most assessors don't get stroppy about contributions from the supporter, they just want to get through so they earn as much as they can.
If you need the loo or to get up and walk around, fetch a drink, say so. You are in control not them. Though most people have a drink to hand ready.
Hope it goes OK,
Denby