For a criminal injury compensation claim directly against your attacker, you will need to prove that the assault took place, and that it caused the injuries you are claiming for.
The first of these requirements will be proved automatically if your attacker has been convicted of a criminal offence in relation to the attack.
This is because criminal cases require a higher standard of proof than civil cases (‘beyond reasonable doubt’ instead of ‘on the balance of probabilities’). As such, evidence satisfying a criminal court will be enough to prove liability in a civil claim automatically.
For criminal injury compensation claims against a third party, it’s slightly different. You will have to prove that the third party owed you a duty of care, that they failed in that duty, and that this failure caused your injuries, or contributed to them.
For a CICA criminal injury compensation claim, our article here explains the requirements and the process involved.