The CAA website for Class 1 says:
Applicants with asthma requiring medication or experiencing recurrent attacks of asthma may be assessed as fit if the asthma is considered stable with satisfactory pulmonary function tests and medication is compatible with flight safety. Applicants requiring systemic steroids should be assessed as unfit.
So IMHO if you have a change in severity or frequency you become unfit. ie need to discuss with your AME before flying. Inhaled steroids are OK