depends on catergury. there is 4 a,b,c, and d.
a = fire, to be crushed
b = chassis damaged bodyshell to be crushed
c = cost of repairs outways value of vehicle, repairable assest, insurer decided not to repair.
d = constructive total loss, repair cost close to vehicle valuevalue person requested it be deemed beyond economical repair.
Cat d you dont need to tell your insurer cat c may need a vic check and a new MOT aswell. Most companies dont mind but like you say some lik enorwich union do put a load on.