I am a solicitor in Scotland. How much was the damage to your car?
From your description it's the contractor which has been negligent by failing to signpost and/or cordon off. You should give them 14 days to accept liability or you will raise a simply procedure action in the sheriff court for your losses. You will have to get an invoice or at least an estimate for repairs. Under £5000 you raise the case in the sheriff court under simple procedure. You can get the forms and details of the procedure at www.scotcourts.gov.uk. Happy to discuss further. I hope that helps. Please leave a positive rating so that the site credits me for my time.