I decided on my diagnosis a short while ago to take up swimming and I went for the fourth time today.. I'm pleased to say I think I am seeing an improvement already. On my first session I basically spent most of the time coughing and hanging onto the side getting my breath back! I felt like I wanted to make an announcement to the other pool users that they wouldn't catch it!
But.. today I still coughed but not as much and the stops were shorter. I also managed to do more lengths. I'm really hoping the improvements carry on!
Thanks to all who recommended swimming and also active breathing technique (although that is still work in progress, I've not perfected the huffing yet!)