Curiosity has the better of me.
Why on earth would having only one kidney make any difference to holding a CPL or ATPL. Single kidney'd people live totally normal lives. I mean single healthy kidney.
I regularly treat single kidney'd people in my joband look at their test results and you can't tell from anything except the scar (if it was removed) that they only have 1 kidney. You can not tell at all if they were born with only one kidney. You have to do scans of various sorts.
Even whole 2 kidney'd people can have one of them not work well and you may never know.
Having only one kidney doesn't have any increased risk of kidney failure overall or at least not failing suddenly so as to affect a flight. If you get renal failure (just as 2 kidney'd people do) the effects are relatively slow onset.
In case your wondering about the soap-box sounding statement - No, I'm not a single kidney man but I'm missing something about the UK rules.
Any enlightenment?