Premise: In British English it is no longer considered a solecism to use the plurals they, their, them, theirs as a generalized pronoun for words like eyeryone, everybody, anyone, anybody , etc.

Hypothesis: It is still a grammatical mistake to use the plurals they, their, them, theirs as a generalized pronoun for words like eyeryone, everybody, anyone, anybody , etc.
Relation: contradiction