In the event of an accident, instead of paying for the full repair, No matter how extreme the damage, the most you will pay is the insurance amount. All you need to provide is a police report to show the damage. 

Yes, If a police report is raised, you will most likely be charged the full excess amount. In rare cases, you will be charged less. 

Please note it is a breach of contract to fix any damages at an outside garage and not at the official dealer workshop, repair charges will still apply.