From reading franks cover of this in lrm the first mistake you made was claiming off your insurance . They can wright off your car . If you had claimed direct of the driver at fault you are then the third party and they can not wright your car off they have to repair it regardless of cost . I hope you can get this sorted . Your other option is to ask them for an offer where you keep the car and get a payout then you can use the money to repair the defender . My uncle did this and it worked out the best deal , and he got to keep the vehicle he new and trusted . I belive they call it a for salvage settlement