Actually not all councils are insured for tripping claims. Many self insure and if they have robust maintenance systems they use section 58 defences to resist claims. The premiums are excessive.
From Brighton Council website....
Public liability insurance claim
If you have had an accident on the public highway and wish to make a claim against Brighton & Hove City Council*because you believe the council has been negligent,*please inform us by completing the*public liability claim form...