[Closed] Rear end collision and third party disputing - any experience?

I got shunted from behind at a roundabout (guy behind me obviously looking right and anticipating me setting off rather than watching me). It is with the insurance companies and what I thought would be a cut and dry case looks like becoming a dispute. Third party is now stating that I pulled out from the left and collided in to him. There are no witnesses.

The damage is to my drivers side rear corner and his passenger side front corner.

Before submitting my response I thought I would canvas opinion here.

Cheers