Looks like James Lock Hatters have an online shop -

http://www.jameslock.co.uk/index.taf

They have quite a range of hats on display here, plus instructions on how to work out yout hat size in the FAQ section.

Great tale thanks!

Despite coming from Essex I can act posh, however my cheap ASDA (Walmart in U.S. I think) suit will give me away!

Do they make a burberry style one?