I took the B in Singapore and there was a bit of a scandal because, as the story went, somebody had phoned a mate who was taking the exam in the UK seven and a half hours later and had read him the question paper (pricey and difficult to organise in 1967, but not impossible). Never did find out if it was true.
Later on in my career about half a dozen of us on the squadron were told to report to the CO's office one day . Once in we were told that he had discovered that none of us had applied to sit the C exam, and that we were to go and get our applications in straight away, no excuses. Well I passed, not that it did me any good as I never advanced any further than flight lieutenant.