According to the CAA document detailing respiratory requirements you need to satisfy the following for a Class 1 medical:
FEV1/FVC Ratio needs to be more than 70%, not just FEV1 - there is usually a marked difference between the two with FEV1 being the higher figure by quite a margin (well in my case anyway)....An FEV1/FVC Ratio of less than 70% needs to be examined by a specialist in respiratory disease.
For a Class 2 medical you need to have a peak flow of more than 80% of your predicted value, anything less and once again this will be reffered to a specialist.
Hope this helps....
WTFH