I received a caution/fixed penalty for this incident – that should be the end of it
This claim is entirely separate from any criminal proceedings. The caution or fixed penalty was the conclusion of the criminal proceedings.
This is a civil claim for compensation by way of damages to cover the costs incurred by our client as a direct result of your action.
In order for you to receive a caution you have admitted the offence to the police. Your admission will be admissible in evidence in the civil proceedings as evidence of your wrongdoing and should establish liability.
If you received and paid a fixed penalty, whilst this does not involve a formal admission, you are given a formal opportunity to be tried rather than pay. The decision not to seek trial is a fairly good indicator that there was no dispute to criminal guilt.