Just got my Class 1 and I have Asthma.
It depends on what triggers your symptoms and how bad they are. Expect to go for a run round the car park and do 3 spirometry (sp?) tests.
The key worries they have appear to be if it is debilitating in any way, if it is triggered by cold air or by stress. Other than that you should be ok. I worried about it but the staff are very helpful and explain everything to you.