I am writing this in the hope that it may help anyone who may find themselves in the position I was in regarding a PhD viva ‘difficult situation’.
I attended my viva expecting minor corrections. I, and my supervisor were confident with this. To cut a long story short there were significant procedural errors concerning the viva; the viva was poorly managed, the external examiner was unprofessional and aggressive and the independent chair not in control. The result was R&R. I was gutted. My supervisor was furious.
I appealed the result with the full support of my supervisor. I was unsuccessful and submitted an appeal to the OIA. Due to the time scale of the OIA, I had to undertake the R&R- which I did.
I was offered an MPhil – due to reasons, which were not questioned/asked for in the re-submission. There were significant questions concerning the marking of the re-submission, which resulted in a further appeal to the university, and subsequently to the OIA. I sought further advice at this point – Daniel Sokol provided advice and support, and I am sure it made the university realise I was serious about my complaint.
The OIA concluded that there had been significant procedural errors throughout, and the University offered me a new re-submission. The ‘new’ viva was a totally different experience, the examiners were interested, professional and fair. The result – minor corrections, which I completed, and were signed off without query. All in all a very different experience. I attended graduation, and got the certificate too.
What I learnt – don’t give up, get support from your supervisor (if possible), get advice from the Student Union, and if you feel it necessary, and you are able to, I believe legal advice will make the university realise that you are not just a disgruntled student, but a prepared and committed disgruntled student.
The process has taken me two years. Two years of stress – and yes, I could have walked away, with nothing. But, I was not prepared to do that, not until all options had been investigated fully.

Thanks for posting this - it's really good to hear that vivas outcomes can be successfully challenged. Well done for persevering Dr!