Continuity mistake: In the programme shown on 11 June 2007, David Platt takes his exam and then sets fire to his exam paper. In the programme on 22 August 2007, he collects his result and gets an A. He could not possibly have got an A, as he set fire to his paper.
Suggested correction: He could very easily have re-taken his exam. That is very much allowed in the UK.
Yes, but if he blatantly set fire to his exam paper in the exam hall, it's most likely he would have been disqualified from taking any subsequent exams.
Well, we simply can't be certain of that. Plus it's a soap; things aren't always grounded in reality, and things need to happen to characters (like passing exams) no matter what. Clearly, he was allowed to re-take the exam, and we're all just gonna have to deal with that fact.