AMBER means 'Stop' at the stop line. You may go on only if the AMBER appears after you have crossed the stop line [or are so close to it that to pull up might cause an accident.]
The last part of the rule, which I have enclosed in [ ], is the real problem. This part is open to individual interpretation. It leaves the driver to decide whether too close to stop, and a following driver to judge whether the car in front will stop, or continue on.
It then raises the question about being required to have a safe stopping distance from the vehicle in front so that you can safely stop at all times, which means that the car stopping when very close to the line SHOULD NOT result in an accident.
From the point of view of the learner-driver under examination, this leaves him in an awful situation. He will be adhering as close as possible to the letter of the law, so it is almost certain that he will stop at the AMBER if it is at all possible to do so before crossing the stop line.
On the other hand, the examiner may well be calculating a possible accident scenario and, if a vehicle was following, very possibly ignore the "follow at a safe distance" rule, and instead apply a 'fault' decision based on that part of the rule in [ ].
Not everyone would agree with me, but I have always felt that the GREEN light should start flashing for about 5 seconds before changing to AMBER. This would give drivers the opportunity to commence slowing down in the expectancy of not reaching the stop line before the AMBER signal shows. It would also serve as a warning to following drivers that they were about to be required to stop.