I had my follow-up appointment today.
I didn't have to wait long to be called. I had done my homework and my bladder was already sufficiently full for me to go straight away. I pissed into a large funnel which led to a bottle attached to some sensitive measuring equipment. The result was that I managed to piss about 380 ml but a further 120 ml or so was left in my bladder. The rate at which I pissed was up to 20ml / second, which counts as normal.
The guy I saw, a young Welsh registrar, asked me about how often I had to get up in the night for a piss. I reckon most nights it's 2 or 3 times. He said it was up to me, as mine is a borderline case and as long as I never have any trouble getting started pissing then they are reasonably OK with it, but they prefer the bladder to contain less than 100 ml after pissing. He offered me the option of some alpha-blocker (tamsulosin I think he said) which would relax the neck of my bladder so that I can get rid of more. Apparently it also has an odd effect on the ejaculation process so that the semen ends up in the bladder rather than the outside world and is discarded when pissing. You will be pleased to know that I won't bother to report back on this - unless someone really asks nicely!
I am going to have a blood test to check that there are no detectable metabolic reasons for me having a kidney stone and he will write to my doctor about starting on tamsulosin.
Discharged!