jono
Your mentioning a theme prompted me to have another look. I then saw it pretty much immediately but I have absolutely no knowledge of it (except that it features in the title of a typically amusing and quirky song by HMHB) so have no idea how pervasive it is in the solutions.
I assume that the theme is 19a 18d, of which I have no knowledge. Tricky puzzle, but doable. Does it have to be international? I have no objection to UK-centric clues, but I am a Brit!
I also had no knowledge of the theme, but Google verifies Ianwil's assumption. I wonder how solvers feel about inclusion of a theme that has little or no bearing on the solution?