Thank you so much everyone for your invaluable help and advice. Our computer has been out of action for a week so apologies for the lack of feedback!
I have to admit we went privately to see the gastroenterologist, and I only got his name cos one of my best friends has 2 sons with really severe allergies and they eventually found him after a long and tortuous journey thru the NHS via dozens of patronizing and ill-informed health visitors and GPs.
Anyway, this doctor runs a (apparently very well-known) paediatric gastroenterology clinic at the Royal Free but also sees private patients once a week so I went to see him privately after ringing his secretary and describing my daughter's symptoms (very small with extremely slow growth) and asking for an appt. This doc's speciality is (non-hormonal) growth-related stuff, I think, but he is also a specialist in allergies.
So I actually went to consult him about dd2's size and to ask if I should be worried (she is 18 months old, 9.7kg and 76cm). She also has eczema (comes and goes but is sometimes very bad) and severe cradle cap (so no hair and a scabby head since birth, poor little mite).
He cleared her size and said she was absolutely fine, just naturally small, but during the course of the examination, and after asking me loads of questions, he told me she had an cows' milk protein related allergy that would eventually resolve itself, but that was causing her problems with her skin and also her digestion (terrible smelly loose stools) and might even be holding back her growth. If anyone is interested I can find out his full title and also the full description of her allergy. We have to have tests done but first one is a stool test which I haven't managed to do yet (have to scoop it into little pot and rush to Gt Portland St at top speed!)
After only 10 days without ANY dairy her skin and head is much improved. I am persevering with the rice dream and she's taken to it really well, so I think maybe she just didn't like dairy that much as well as finding it hard to digest. She loves any protein-rich food (complete carnivore) so am sticking with the rice dream till we see the dietician. Am also giving Yofu soya yoghurts, which she seems to much prefer to Petit Filous. Am also wondering if I can use goat's milk butter for cooking/sauces.
The irony is that I've been stuffing her full of dairy for the last 6 months on the recommendation of my health visitor who told me to give her lots of dairy fats in food to increase her calorific intake and therefore her size...