The way i see this is the same as a business owner if you have a frontage with uneven slabs on it and someone trips over one then as the business owner you are liable.I always thought in british law that ignorance was no defence, if they have a duty to keep the roads in good repair then they should be checking the roads or at least have a department who does it.
If you get no joy that way you could try small claims court and represent yourself. If all else fails then i would just try and cause as much damage as possible there are quite a few councils that now use ISO9000 accreditations if they have a department that deals with roads who haven't spotted a fault ask for whatever they call a quality occurance report form (anyone can do this under the rules of the ISO accreditation) anyone with the ISO hates being QOR reported as it causes them no end of hassle chasing it up and it will go up the chain. It may seem alot of trouble but it will give them more of a headache than you