OK, so I found a UK bricks and mortar retailer that stocks RE (a shop called IRIS with branches near London Bridge and in Richmond). I tried on a pair of 52s and 58s, they didn't have any 55s in stock (most popular model apparently).
I'm still not sure about sizing though, my temple width is just under 130mm but my head size is nearer 59cm, which gives me conflicting advice from here: http://www.themandonstore.com/product/228/product-details.html
Also, both of the 52mm and 58mm seemed to bow a bit in the stems (arms) of the glasses and I wasn't sure if that was normal or not. Anyone?
What! I can hardly believe it. Thanks jonc. This is what SF is all about.
I tried just about every shop in the centre of London last year. Most hadn't heard of them. The ones that had, had replaced them years ago with American Optics, swearing that they were of the same quality.
I'll check them out
Edit: Another great independent shop for Persol and others (not Randolph) is: http://www.adamsimmonds.co.uk