Hi Daphne and welcome :)
I went through so much with my claim for ESA/Incapacity benefit last year I think I could write a book about it!
I too was - still am, agrophobic and suffer from 'major depression and anxiety'. I put in a claim for ESA in october 2010 - got it, great! The I had to go for a medical assesment in the November - no way of getting out of it, so my fiance had to take the day off and take me in. I was a nervous wreck, but I got through it. It didn't even cross my mind that they could dispute the fact I was ill, but in February 2011 I had a phonecall out of the blue saying that they could see no reason why I couldn't work full time

I could not leave my house alone so how was I going to manage to work - when it was mostly anxieties about work that had seemingly got me here in the first place?! I (with a lot of support from family and friends) disputed it.... got the paperwork through which stated that because I was wearing clean clothes/wasn't rocking backwards and forward/kept eye contact/'showed no ideals of self harm or suicide' (which I wasn't even asked about. I had a long sleeved top on so there was no way he would have seen the scars on my arm anyway) - I was able to work!

Because I disputed it they carried on paying me a smaller rate of ESA every week - I think it went from £92 to £65. I went to the tribunal in July - easily one of the scariest things I have ever done. Luckily my parents were able to come with me and the desicion was very quickly overturned. I had a rebate of the underpayment and because they had seen me for themselves, I no longer had to produce medical certificates - not that they would really accept them as proof that anyone was ill anyway! If they had, I would never have had to go through all of this! The proviso was that I would attend a 'work-based interview' every few weeks in the local job centre 20 miles away.... That is incredibly nerveracking every single time - but the lady I see is so incredibly friendly! She knows I'm nowhere near ready to go back to work full time and was so angry I was put through all of the above and was ecstatic when the desicion was overturned. I don't think they are in any massive rush to get you
back to work in those interviews - they just monitor you a little bit.
I know - through the lady at the job centre - that the whole system in changing in April anyway. I have recently had to do another medical questionare which could result in another medical assesment

But... at least I know what to expect this time! Not sure I could go through the whole thing again though. There has been a fair bit on the news over the last year or so about how the medical assesments are changing because they are basically ridiculous! So I hope they are changing for the better!! As I'm sure you know yourself from the questionaire theres not a lot of consideration given to mental health issues.
I'm sorry I couldn't have given you a more positive account of my experience with it all - but as I say, it is all changing over the next few months anyway. The work based interviews are nothing to worry about (apart from our own issues with agrophobia) in my experience they are not there to force you back into work.
Please feel free to pm me about any of it - its a truly awful thing to put anyone through, nevermind those of us that are struggiling to cope with the most basic of things in daily life.
xx