What is the test for adduced evidence of bad character?

It is a fundamental rule of criminal law that evidence of disposition or propensity adduced solely for that purpose is inadmissible. As Lord Simon of Glaisdale said in his speech in Director of Public Prosecutions v. Kilbourne, [1973] A.C. 729 at 757, 1 All E.R. 440 at p. 461: All relevant evidence is prima facie admissible. The reason why [evidence beyond the indictment of bad character] is inadmissible is, not because it is irrelevant, but because its logically probative significance is considered to be grossly outweighed by its prejudice to the accused, so that a fair trial is endangered if it is admitted; the law therefore exceptionally excludes this relevant evidence. . . .