Hi J,
the 58 Defence is a valid one for county councils to use - after all they are the largest landlords in the country and cannot be expected to repair every defective paving stone, pothole, cracked step unless someone has reported it to them and they have failed to act. otherwise, the system of inspection is a valid Defence ie they inspect said road in set intervals and if there is no defect present when they last inspected it then they can repudiate your claim.
as someone else said though sometimes they will crumble after you have issued proceedings once they see your evidence ie photo's of pothole, photo's of damage, repair estimate and invoice as they dont want the hassle but on the other hand they may fight it all the way - depends on the exact council and the advice the county solicitor provides.