Firstly, stop in a safe place and put on your hazard lights. Call the police and ambulance service if anyone has been injured.
If you are fit to do so, note down the number plates of any vehicles involved, get the contact details of the other drivers involved as well as any witnesses, and take photos of each vehicle and any areas that have been damaged.
Once you've done this, call our claims line on 0330 088 3838. You'll need to select option 1, then option 2, and then option 1. It's open 24/7 all year round.