There's no official list of serious faults as far as I'm aware. A minor driving fault can develop into a serious or dangerous fault. Faults which could lead to potential accidents will be classified as serious faults. For instance if you emerge from a side road without looking carefully and a car on the main road has to perform an emergency stop because you've cut through, this will be a serious fault and you will fail your driving test.
If you have any more concerns, then let me know.
