I recently tried a pair of the Junya Trickers from Mr. Porter. I take a UK size 10 in the 4444 and 4497 country lasts so ordered the size "Large" which equates to a size 10 (according to the web site and on the inside of the shoe). The information given to you by Trickers is quite correct, they are half a size smaller than that marked. I had to return mine as they were too small with no toe wiggle room at all!
I hope this helps.
Great stuff, thanks Rob - I didn't see this when I posted earlier....