I think it depends on the models you're comparing. The UK only produces the GT version, so of course one can compare with a T (luxury version), or an S (sports version) from Japan and find differences. The ST is the equivalent to the GT.
My boyfriend just got an ST and
-It has 18" wheels (just like a Uk car)
-Brembo breaks (same as above)
-6 speed manual gearbox ...
-xenon headlights...
-heated seats ...
Not sure about other differences as my technical knowledge is (still) quite limited... but I'm keen to learn more about the 350Z, it's a wicked car!
Just wanted to point out that it's not fair comparing the differences is you're doing it between a Japanese base model and the UK GT. Would be fairer to compare ST against GT.
Oh yes, I'm a newbie... I'm not very good with introductions, but hope to be around for a bit and get to know the Z a bit more.