Jonesy - you said:
For ground roles, you need to have been symptom free and therefore without treatment for four years or more.
Not quite true:
If you suffer from asthma or have done in the past, you cannot be considered for flying branches of the RAF. For ground branches and trades, people with a past history of asthma, wheezing or inhaler use may be eligible for service following review by medical staff. If you have current asthma symptoms or a current prescription or you use an inhaler for asthma or wheeze (regardless of cause), you are not eligible to apply for service.
which is taken from the download from the RAF site
http://www.raf.mod.uk/careers/rafcms...A28D2D8DAE.pdf