Chambers gives AN as "(obsolete) preposition; a form of on" so if you excuse the lack of an "old word" indicator it just about works. Perfectly fine puzzle but way too many nonsensical surfaces for my taste.
A really nice puzzle as a minimal amount of grid staring was required for the endgame. A good mix of clues, some difficult, some not so, made it a reasonable challenge. Thanks Skylark.
I've ground to a halt with gaps in the SW corner. A hint for 17d would be appreciated: Chair over bar contains navy stud (8); a letter to be removed before solving.
The letter to be removed is in the first word, leading to an old crossword favourite. That gives the first two letters of the answer, over leads to the next one, then a bog standard 'bar' has 'navy ' inside. The stud is a thing, not a person!