My reading of the rules is that if your asthma is controlled you only need these tests if you are on regular inhalers or have been in the last 2 years (class 1) or 5 years (class 2)
The reactivity test is simply 6 minutes of exercise and a before and after FEV1. The spirometry means blowing into a spirometry machine. Both these tests are normally undertaken by a physiotherapist in hospital and the fee should be about £50
The problem is that the CAA wants them done by an accredited specialist ie a consultant and that is why the cost rises. Goodness knows why as the machines provide a printout which could be sent off, and a physiotherapist is licensed and regulated and thus as 'trustworthy' as a consultant