I've said it before and ...... go and see a lawyer. He'll tell you to send a letter to your insurer informing them of what has happened and to mark it " for file reference only". That way your "No claims" is safe.
You then visit the bus company and ask them if they would like to compensate you directly or have you make a claim.
Warning:- Direct settlement is quicker but if you later find some damage that you didn't know about when you settled then your stuffed. It's best for write offs as you get the money and can keep the car and sell the parts and get enough to buy a better motor than you had. We went from an old 608 Merc to a recent Iveco 7.5 Magirus Deutz truck with tail lift and had money left over for MORE BASS BINS.....WHOOMPA WHOOMPA

If you need something done quickly just ask a busy woman then get the f"k out of her way.