Dragstrut, I had a very similar experience some years ago when I first applied for a Class 1... Like you I had been diagnosed as being asthmatic as a child, despite never having an "attack", and had been on numerous inhalers over the years.
Anyway, to cut a long story short I ended up persuading the CAA (thanks to some help by an eminent professor in this sort of thing) that I would never pass a normal lung function test using a hard blowing method, and instead would pass using a long slow blow... The CAA accepted this and I am now a Class 1 holder.
Hope that helps!