Ultimately, whether or not the authority you're attempting to claim from has a defence under Section 58 is for the Court to decide. However, you can assess their defence yourself to see whether or not you think you could make a case. Always keep in mind that their defence might be quite robust and you might not win.
Armed with your FOI information, information about the scene, and your copy of the national code of practice, these are the key questions you need to ask in relation to your claim;
Whilst it is your decision whether or not to proceed any further, if you honestly answer "yes" to all the above, your claim is probably not going to succeed.
If there are any discrepancies, however, the best course of action is to write back to the authority or the claims handler, pointing out these discrepancies and including evidence in the form of paperwork and/or photographs. Inform them that you don't consider that they have satisfied Section 58. Making threats about solicitors and Court at this point probably won't help, and you might want to wait for their response first. Again, be very careful with what you write and/or say.
If you do find a discrepancy, don't assume they will now simply pay you. There could be a perfectly reasonable explanation for the discrepancy, or you might have mis-interpreted the information. They might even be happy to defend the discrepancy in Court.
If the authority still refuses you claim, you will have to decide how to proceed. Small claims are a popular and cost effective way of taking action for small amounts, and they can now be completed online at www.moneyclaim.gov.uk Always keep in mind that you could lose the case and end up spending out more money. You might even want to take some legal advice at this stage.