It's very, very sad, but I'm convinced that 99.9% of British athletes are clean. I was involved in junior-level (up to U21) coaching for many years. Every single child who entered our club was given a card listing banned substances, which they duly showed to doctors and chemists. Random testing, e.g third place in the U17's 100mH, meant that quite often they were tested, my daughters amongst them. Never once did anyone have a test with anything at all suspect on it. 2 athletes out of the thousands in the North (of whom we all had suspicions) were eventually caught and banned - one on the verge of becoming a household name, but she was caught.
I don't think I'm being naive when I say that this was the norm. It is horrible to think of cheats spoiling a sport which I love and think has something to offer to everyone - running, jumping and throwing things are natural activies and even the non-sporty child can take part in sports day if there is a race-walk.
I'm very sad that the international authorities have not got control of this situation.