This BMI thing is a load of old Bullocks!! Because take a body builder. They will be, for example, 5'10" tall and weight about 20 stone 10lbs. The BMI calculator puts him as having a BMI of 40.5 and say that he is seriously overweight. Yet that weight is all muscle and he is probably extremely healthy.
Taz, you do karate, so some of your weight is bound to be muscle. So I think we should all go with what we feel is normal and our dress size and not some silly BMI chart.