Just to hijack this thread slightly:
I would have found it really helpful if someone had actually told me, 9 years ago when I learned to drive, that the amber time is 3 always seconds. As far as I know, it doesn't say this in the highway code or anywhere similar, it isn't taught, and almost no-one I know knows it either.
I only found it out when I came to this site. (Obviously, I noticed ambers were a few seconds, around 3, kind of. But I never realised they were exactly 3 and that you could rely on it.)