I don't know if this helps at-all, but about 8 years ago I started to suffer from moderate hayfever (after some blighter planted a field of oilseed rape next to my house). I initially used a quite effective antihistamine called Triludan (Terfenadine) that was recommended by my GP, but a year or so later it became prescription only due to lots of people having side-effects (not me, I was fine).
Casting around for an alternative (okay, I could probably have got a prescription, but didn't try) it was suggested to me that I try high doses of Vitamin C.
So I gave it a go, and it works wonders. Through the hayfever season I take about 2000mg per day - it takes about 3 days for the effects to kick in, and if I forget to take them about the same to notice. But, it pretty much completely eliminates all hayfever symptoms.
Being a cautious soul, and not medically trained, I discussed it with both my GP and an AME, neither could see any adverse effects to taking this sort of quantity of vitamin C, so I carry on. Works for the cat-allergy that appeared about the same time as my hayfever as well. Oh yes, and I've also listed it on my class 1 renewal form, without a raised eyebrow.
I've mentioned it to several other people who have tried it, and it doesn't seem universally effective, but certainly some others have also found it effective (and, relatively speaking, cheap - I buy big bottles of 1000mg capsules (more the size of suppositaries, but they are easier to swallow than they look) from Holland and Barratt).
G