Lumen, I found that name bit a bit ... clunky, unsatisfactory. Ignore what's in the perimeter, just think of the formal name of 4,6. My 4 D was just a guess, seemingly straightforward - and it's in Bradfords under 'informer'.
Amazingly I've actually finished totally. How satisfying! The only clue I'm not sure of the parsing is 7D. Glimpse spot on out of date chard. The H is to be removed before solving.
All completed, nearly, in record time for me but left 2 unsolved clues which I still can't see today. 20a Arizona blackboard displays mathematical symbol (5) and 24a Chance to hit anti-tank battalion (5). Help please.