Could be your occupation. My son has 2x NCB at 24. His insurance on a Z is about £2800ish as a serving soldier.
Change his occupation to Computer Engineer and it drops to £800ish
Insurance logic:
Computer Engineer will use his car daily, park it publicly, and even park it in dodgy areas from time to time - Low risk
Soldier parks his car on a Military Base, guarded by men with guns, high fences and razor wire. Rarely use the car. Park it up for months on end - High risk.
Dicks.