I need a new pair of boots and OK I only had 2 shops close today . I went first to Deichmann and their 6 is a 40 but 5 is a 38. I couldn't find any 39s and the 38 fitted but a bit snug.
I went to M&S and tried on a size 6 or a 39 , I could have worn pairs of of thick socks in them. I ended up buying a size 5.
I've been a 6 since having my daughter who's now in her 30s. I've never had this problem before.