I really am a complete idiot. Having assumed - quite baselessly - that the endgame required some knowledge of football competitions, I put this aside after completing the grid and the teams (heavy use of an online anagram solver for the latter). Having looked again at the preamble, I finally grasped the bleedin’ obvious and polished it off. Many thanks to Harribobs for a thoroughly entertaining puzzle - and for some self realisation!
Actually, there was no need for anagram solvers. As the possibilities were limited, all I did was identify a less common letter in the anagram, e.g. w, and then run through the lists.
Filled the grid, thought I saw what the preamble was getting at, and thought "Surely not!" But it was indeed the case - very impressive construction, and a nice set of thematic clues.
A list of relevant teams was very helpful for this non-fan...