Insurers will always prefer you to use one of their Approved Repairers to repair your car. They will argue that their Approved Repairers are carefully scrutinised and appointed to provide the highest customer service and quality of repairs for their customers.
They may also throw in other benefits – such as the Approved Repairer will provide you with a free courtesy car for the duration of repairs. And Authorised Repairer repairs will be carried out in accordance with recognised industry standards, guaranteed for 3 years and all replaced parts are manufacturer-approved. Further, Approved Repairers can usually start work more quickly as the need for sending estimates into the insurer to get them approved is removed (the insurers can often see the damage to your vehicle via video technology in the repair shop).
But having said that, you do have the choice of using your own repairer. Doing so means though that the insurer can’t guarantee the work and you will need to obtain an estimate for them to approve before work can commence, so it might take longer. And you may lose your right to a courtesy car.