From the bump ive had, the solicitor said as clear as day " if theres a bump on the front of one car, and the rear of the other - its the fault of the driver from behind".
I was hit from behind, and had to claim through it and it went smoothly due to them accepting liability. They said the chances of the other party winning, even if they disputed it were slim.
However your best chances here without onboard footage would be a 50/50 i would think.
A few years back you'd get people coasting along, then for no reason slamming on - trying to catch the driver behind out so they could get an easy claim
