I don’t get it from aircon no, I assume it is caused like people have suggested from breathing cold, dry air through the mouth. When I’m in a place with air conditioning Im not usually doing much exertion so my nose warms it up first. I suppose in people with regular asthma it may be though, I don’t know, I’m no expert.
As for the viral infection I don’t think so Axeman as I have had this problem since doing school cross country runs in winter so unless it’s something really persistent it’s probably not an infection.
Anyway thanks for the tips and information everyone, having read about exercise induced asthma on the internet it seem to be what I have so I think I’ll be trying to breathe through my nose more in future and try putting my buff over my mouth as well.