Interview under caution

I have a letter telling me to attend an 'Interview under caution'.
It is apparently to do with my claim for ESA, JSA and Housing Benefit. none of which I am on any more - got enough work I can actually do a few months ago.

I am not sure what it is about, but I must have made a mistake *somewhere* - I've done lots of odds and ends of talking about my experience of living with schizoaffective disorder to professionals and researchers. I thought I / my partner had declared them all, but I have substantial problems with memory and organisation, being bad with money is a symptom of bipolar, and it is entirely possible that I messed up somewhere.

What should I do? Who should I take to the interview? It says I can bring legal representation, how can I sort this out?

My partner has anxiety, and he's having meltdowns that we will both go to prison for ten years. I am trying not to think about that. If I've screwed up I'll happily pay the money back. I know I can't cope well with forms and talking to strangers on the phone and managing my own money, but there doesn't seem to be anyone who can help me to do it right reliably.

Feel terrible about this. Both of us had really got our lives together in the last couple of years, I've been doing more freelance work, my partner has started a new job, and we've been off everything except my PIP for the last few months. Then just as I thought we were safe from the brown envelopes, this happens.

How do I find the sort of lawyers that deal with this? Yorkshire.

The letter says I need to arrange for an 'appropriate adult' to be with me at the interview.
I don't know who or how. My partner is too scared and would just cry all the way through. I don't know who else to ask. I don't have a CPN or social worker or anything like that.
I'm not sure if I will be able to talk at all. When I am too stressed than I cannot talk, especially to strangers.