I'm from the UK too and have also been struggling with this terrible heat wave we have been having! Even now it has cooled down, it is still WAY too humid! These thunder storms haven't been helping pain levels either

I haven't really found a way of 'coping' with the heat in the 6 years that I have had RSD. I do tend to take cool baths, although these can sometimes cause pain to get worse

I really hate the summer as I have blood pressure / heart problems (POTS) and the heat seems to make it worse.

Sorry that no one seems to have any answers as to what might help... RSD is such an horrible condition Just know that you aren't alone and I hope you are feeling better soon! Hopefully the temperatures will cool down a bit!