Yes, the half-sizes tend to be a bit trickier over here for some reason. I also
usually wear a 6.5 here (
always a 9 in the US), and to get a 6.5 generally means shopping at Clarks, for me. I've tried on 6.5's at M&S before, but they tend to be too narrow for me there, and the wide ones are too wide!

I think the British sizing, for reasons unknown, doesn't seem to be very consistent from one shoe to another. Plus, I don't understand why shoes here don't seem to have the various widths available?

However, in general, I have found the British (to American to other international sizing) conversion charts wrong more often than not - usually saying I would wear a 6 or a 7 here, and I most clearly do not. I wonder if that's because the half sizes are harder to come by, so they're trying to jam you into whatever size is widely available - which is, unfortunately, too small or too big. I don't know.
If you can find a shop that sells international/European sizing, I know that I will always wear a size 40 (just like I always wear a size 9 in the US), you might have better luck with that. Schuh carries some shoes with international sizing, and you occasionally find athletic shoes (trainers) or walking boots like that too.