I think the UK is more progressive than your more puritanical cousins, the US. You certainly have much better insurance support for transition than we do (and I'm guessing your anti gender discrimination laws are better too), and I'm wondering if this makes a difference in how people in the UK generally see TSs, which then extends to CDs.
Also, the guys you speak of who get a good laugh at the Halloween parties ... are they dressing for real like the CDers here would be, or are they doing it on a lark with big inflated boobs, platinum wigs with beard showing, etc? Men in the US do this too and they also get laughs if it is obvious to others that they are making a parody of CDers.