Got rear-ended at a roundabout last week. Other driver claimed I reversed into them. Their insurance was trying to go 50/50.
Sent them my dashcam footage showing clearly they drove into me while I was stationary. Claim settled 100% in my favour within 24 hours!
If you don't have a dashcam, get one. Best £50 I ever spent. I use a Nextbase 322GW - highly recommended.