I have been on one of these very recently in the North West (nearly exactly 3 years after my last one - which was lucky). The instructors were very clear that Admiral were currently the only firm they knew of who were putting premiums up if you disclosed, but they were equally clear (saying of course that they couldn't possibly encourage you not to disclose if you were under a duty to etc...) that if you didn't disclose Admiral had no way of finding out. They were very animated about this actually urging those in the group with Admiral to make a point of switching companies at renewal time and telling Admiral the reason was because they (i.e. you) had heard that they up the premiums for attending speed awareness (etc) courses. The instructors were firmly of the view that if Admiral get away with it, then it is only a matter of time before all the other insurers do the same.
Its a bloomin cheek when you think about it, because you have not been convicted of or admitted any offense by taking the course.
As an aside, the course itself was actually very good. Thought provoking and interesting. Not at all patronising. Very useful in fact in terms of improving roadcraft and anticipation skills which can only be a good thing.
go with an open mind.