I have a DS who is severely dairy allergic. (to the point of anaphylaxis.) He is also allergic to Soy.
My GP's at first point blank refused to prescribe ANY suitable formula for him. They recommended I try him on almond milk. He went into anaphylaxis. So now Nut allergic too.
It took me 3 months after HAVING to stop BF (due to having to go onto other meds for my epilepsy incompatible with BF, had to stop overnight.), and getting nearly £500 in debt by not paying my bills so I could buy him the Nutramigen 2 advised by the HV (I had been on a dairy free diet since he was 8wo on advice of BF counsellor due to severe colic and reflux in DS3), before they accepted that it was just a financial impossibility for me to afford to buy milk that wouldn't KILL my DS when I am an unemployed Lone Parent on benefits. 
They decided to prescribe him 6 x 400g tins a month. Bearing in mind it is his only milk source, and I have to use it in his cooking too. (can't use Soya replacements due to Soy allergy). I was actually getting through 10 x 400g tins a month (the tiddly ones, and they cost £15 a bloody tiny tin...), so was still paying for an extra 4 a month, costing me £60 a month.
When the GP tried to drop the scrip to 4 x 400g tins a month, I had a massive hissy fit minor emotional breakdown in the GP's surgery.
.
They kept it at 6 tins a month.
On the plus side, they cocked up massively, and somehow sent a scrip over to the pharmacy for 30 tins. 24 of which can be renewed after 4 weeks. God knows how that happened, but I will only ask for 12 next month (split scrips)...
It has taken me 11 months to get a referral to the dietician, and he STILL doesn't have an appointment with the allergist, as the GP won't refer me. I started asking for an appointment with both the allergist and dietician in July last year. His Dietician referral wasn't put through until the 30th May this year (budget apparently...), until I stamped my feet and had another hissy fit at the GP's, receptionist must hate me! got cross, as he has other, more minor allergies, and as I am having to introduce each 'new' food VERY gradually, I don't know what to feed him half the time.
I still can't even get the GP to refer me to the allergist - something to do with the fact that as the waiting list is over 18 weeks, they can't refer until it gets to that point. But it won't, because not all GP's have stopped referring. So I can't even get skin tests done to find out what else he is allergic to, so I can bloody avoid it!!
AAAAARRRRRGGGHHHH!
Dealing with GP's budgets and allergies, even life-threatening ones, is just soooooo damn frustrating.
And Saggy< I didn't realise your DD was coeliac! DS1 is too. Though it took just 6 years to get the final diagnosis from first cutting out gluten...and I never got anything on prescription either. Not surprising with my GP's though, as if it is this hard to just get milk that won't kill DS3, something that 'merely' causes DS1 internal bleeding is hardly likely to be a priority,is it...