The nurse told me that the pain would only be a 2 or 3 out of 10 when she put the first catheter in. It was more like an 8 or 9, and the test had to be abandoned because she couldn't get the tube in my urethra and it was causing me to bleed.
If I had had the time again I would have asked about risks, and what they would do if it was too painful re pain relief (the nurse said they can't use a local anaesthetic gel because it affects the test).
I would have asked what to expect (I wasn't expecting blood, and it would have helped if she had told me once she had finished, so I didn't get a nasty surprise when I was cleaning myself up).
She said that most people don't have the experience I had, but I would want to know what they would do to help if it was that bad again. Looking back it would have been helpful if I had been given permission to say 'stop' - I felt guilty that the test hadn't worked, and I should keep letting her try.
I was put on antibiotics straight after, and told to get strong pain relief from my GP for when they re-test.
(My GP fortunately told me not to go back for a repeat attempt and referred me for a cystoscopy under a general anaesthetic so they can see what's causing the block without the intense pain).