I've just sat my first module of exams (doing Cabair Modular) and the last 2 weeks before the exams my averages and such shot up, the instructors always said that on the whole everyone does better in the real thing than in their mock tests. Everyone feels a bit like you do before they walk in and do the real thing
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I've heard good things about bristol, my PPL instructor did all of his stuff there and said they were great.