if you were hit up the rear in an accident it is the other persons fault always is, insurance company will follow this up. it shouldn't affect your no claims, but you do have to declare it.
i had similar accident on the a12, i stopped and the 6 cars behind me didn't. i had no blame what so ever and was the only one gaurenteed a payout. the case took 2 years to settle as the others couldn't work out whos fault it was first.
basically if you hit someone up the rear, your travelling to close and its your fault.