Wow, amazing responses here, thank you all so much.
DD has never been dry in the daytime and until about age 4 was a terrible "toilet refuser", it was a huge battle to get her to sit on the loo, so I put the frequent accidents down to a behavioural problem rather than a physical one. But in the last six months, it has become clear it's a physical issue: she is completely co-operative now and it is still happening.
I am not bothered about nighttime non-dryness, (staying in nighttime pull-ups is fine) It is the daytime issue that I want to concentrate on, though I completely accept that the two are linked.
I will ask for the renal scan, and also a constipation check. I do think that she was constipated (although GP didn't agree) and she's recently been on Movicol (at my request). This has had the effect of getting rid of her protuberant belly, but hasn't made any difference to wetting problem. I stopped the Movicol because I was concerned it was contributing to wetting, but now I don't think it was, so will ask consultant if we should re-start it.
I have read the ERIC website and spoken to their helpline which was useful, thanks.
I will look for those DryLikeMe pads, thank you. DD often wets profusely, so I don't know if a pad would contain it, but it might reduce the amount of changing needed (e.g. not right through her skirt).
DD doesn't really drink much except water - very occasional fruit juice (like once a month or so) and a fizzy fruit drink on birthdays/special occasions (prob about 8 times a year) perhaps a hot chocolate once a month too. No caffeinated drinks. She does eat chocolate though (not every day obvs) and loves it. I hadn't thought about things like that being bladder "irritants" but now you say it, I did notice when we were on holiday we stopped at a cafe, she drank a full glass of orange juice, and then wet herself 5 times in the next hour - I put that down to the amount she'd drunk but perhaps it was the acidity.