I advise you to avoid signing or otherwise agreeing to anything that leaves you liable for the cost of a credit hire car, or forced to attend a court case, if the insurer refuses to pay for the credit hire car. You should also be aware of your contractual duty to your insurer to “mitigate” your costs in any claim, so if an independent gets involved and increases them in any way your insurer or the thirds party’s insurer may refuse to pay.