First of all you need to understand how your car is being categorised - if it is Category A or B then you are not allowed to repair it by law. Category S (structural) or N (non-structural) cars can be safely repaired if done properly. If your car is Cat S or N and you want to get it repaired you can negotiate 'salvage rights' with your insurer, where the value of the retained car is taken away from the value of your claim. You can then arrange to have the car repaired independently but it will always carried an insurance marker on the V5C registration document showing it was previously subject to a claim. Bear in mind that if that's the case, it will be worth less than a non-categorised car and may cost more to insure. If you do not believe the insurer's evaluation of the damage is fair, you are within your rights to ask for a second opinion from an independent assessor.