My experience is a bit dated (2019, pre-full-on-Brexit), so it may not be completely relevant. The UK CAA had an ombudsman who would field complaints when travellers felt an airline was wrong in denying compensation. I, too, got fobbed off with the weather excuse so I filled out a form on the CAA website providing details and my reasoning why the airline was wrong. It took ~5 months but I eventually got an e-mail saying something like “the airline will be contacting you shortly to arrange compensation payment”. Full marks to the CAA in my book.
The current CAA site does keep a non-exhaustive list of “extraordinary events” which would preclude compensation. I don’t see 24-25 August on the list, so maybe that is a starting point for you, Good luck.