Auto Insurance Claims: 3 car, subrogation, rear end

Question
I was travelling on the motorway and the car in fron braked suddenly, i gently tapped the rear of his vehicle (causing no damage to mine or his) then was hit from behind, causing considerable damge to the rear of my car. Where do i stand?

Answer
The person who hit you from behind is liable for your damages.
If there is no damage to the front of your vehicle or the vehicle that was in front of you, then that is irrelevant to the rear end collision.

You'll need to file a claim with their insurance company or, if your vehicle is not drivable, you may want to consider filing with your own carrier and then they will collect the damages back from the other party through a process called subrogation.