Ah, I can remember many a sleepless night where the only thing to watch was Revisewise
which hasn't been aired since about 2005/6.
I also remember during the early hours in the mid 00's. They re-ran 'The Experimenter' which was one of the most tackiest and naffest looking BBC learning programmes of the 90's.
I also remember a science based one presented by a woman (Who I think was called Stella?) who lived in a submarine. I always forget the name of it.