Re: Not quite right
Widely advertised - just means there was a typed A4 size notice nearby, a link buried in the council website to same and possibly a small copy in the local press notice section.
Council planning committee agenda & minutes are a public record - you should be able to go to the office and ask to see them (Door marked "Beware of the Leopard" springs to mind). Claiming you're vexatious is really only going to stick if you're in the habit of throwing FOI reqs at them every day for info that should be readily available via other means.
Your father could also ask a solicitor to investigate any duties and liabilities that have been placed on him without proper notice in respect to the moved footpath. I'm assuming here that the field access path is your fathers property and not just an easement allowing access.