your neighbour should instruct a solicitor. i hate the phrase "compensation culture" being bandied about everytime mention is made of somebody making a claim - no win no fee was brought in becuase Legal Aid (paid for by taxes) was taken away for personal injury claims.
The Solicitor will obtain the evidence from the Council in relation to their street inspection, repairs and complaints records, and that will establish whether there is any liability on the part of the Council. Effectively if they can prove that they've adhered to their inspection regime, and that the defect was not present at the last pre-accident inspection, then they have a statutory defence to the claim. Having said that, there are allegations that can be made of the INspector having missed the defect, if witness evidence can be obtained to establish that it existed pre-accident for example.
Any no win no fee solicitor will give 100% of any compensatino recovered to the neighbour if they win the claim (costs paid by council's insurers). If the claim is not won, then all costs should be written off by the solicitors.
Look on-line for accident compensation solicitors - try to find a firm that says they're actual solicitors. give them the photos and measurements and see what they say from there.
As an aside - councils and their insurers always always deny liability at first - it doesn't mean that a claim won't be successful..... good luck x