Piece of advice, and probably commonsense obvious- don’t let them know it’s insurance replacement til you pay (I guess you’ll get one of those plastic preloaded cards) cos a) a lot of the time you won’t be able to threaten to go to another chain cos it’ll be restricted to one ie the card’ll be comet branded,
and b) cos the insurance company will only be going to pay a heavily discounted price for the credit on the card, so the price of the tv will effectively already be discounted as far as the store is concerned.
If you’re not getting anywhere with a cash discount, you may be able to get accessories or warranties thrown in more easily.
Good luck, it can be fun haggling but you’ve got to hold your nerve and actually expect something to really get anywhere- a halfhearted attempt will just get you fobbed off or given a dusty pack of blank c90 cassettes.