[icarus pacific]

My best take on your situation is also the most obvious one- that you get yourself to a respiratory physician that is also conversant with diving and see what he/she has to say.

While asthma is a contraindication to SCUBA diving, freediving also poses it's own set of conditions, most notably stresses induced by the neophyte attempting to better their time/depth. These stresses can often induce the onset of an asthma attack. When you're in the water and this happens, you better have a few things in order- your hand on the weight belt release, your buddy hauling ass to help you, and luck.

Let us know of your findings as I'm sure that you're not alone in your situation. Maybe giving Howard at that other freedive site also in the UK a call for a referal might speed things along.