Hii im sorry that you are in this situation. 😞
Whilst i think that you do need to thouroughly go through all of the UCL regulations, as each is different.
I had a similar situation doing my Bsc and I was in touch allbthe time with my Pastoral tutors and the Student counsellor, it is this that made the difference I think as they pretty much knew about everything.
I know it can be hard to share our personal situations but it is the only way that they can help.
Once all evidence is in, pastoral support depts at tje uni also see you and the medical evidence, then you are stronger for appeal.
Perhaps they will let you resubmit (Im guessing this of for the Dissertation?) And graduate next year, i.e you submit for assesment deadline next year?
I was offered this option on my BSc.
Good luck and don't be ashamed. They (pastoral) are trained for this and if you have a student counsellor there go make an appointment NOw.
Take care.