So DS now 7yo, had allergic reactions, then got slightly worse and had a few episodes with quietness/ feeling faint, swollen lips culminating in the 'big' reaction last November.
Saw Cons Pead in Feb and prescribed epi-pens, apart form April when DS was really bad with hayfever he has been very well for a good few months. No AH daily or for treatment.
Negative for raised IgE and all RAST tests.
Cons Pead is thrilled with DS, has signed him off and referred back to GP care. If DS continues to show no bad allergic response (not hayfever but to other things) he will eventually be classed an non anaphylatic risk and we won't need epi-pens. 
She said that sometimes the bodies immune system becomes compromised and that can cause problems (eg random allergic response) and the test for some protein (or something) in the blood that can cause spontanious reaction was negative.
So all good.