If you use your insurer, you are bound by the terms and conditions of your contract. If you deal with the other parties insurer directly, you are then compromised because they have a vested interest in reducing your claim. I'm assuming your car has a damaged quarter panel from what you have said. First thing to do is establish the market value of your car. That is the target repair cost. The second is to go to a reputable repairer and see if they can repair, rather than replace, the panel. Do not think the panel is not repairable, a good body shop should be able to repair just about anything if they have the correct skill set and equipment. You can then either use your own insurer or the third party insurer. Advise them that the repair costs are less than the market value, it is not a total loss if the repair cost doesn't exceed the market value. Make them aware of your lawful entitlement (www.honestjohn.co.uk/insurance/coles-v-hetherton-w...u) and their obligations under ICOBS 8.3.3 (www.handbook.fca.org.uk/handbook/ICOBS/8/3.html). Should you not go this route, instruct a solicitor or a good accident /claims management company. Talk them through the above. If they cannot do what you want, do not use them. Ultimately, if the repair cost exceeds the market value, it is a total loss.You may then wish to retain salvage.