I don't think they're different mixes, as such, Val.
On the "I Don't Wanna Leave You" side the intro is shorter (by a few seconds) on the UK copy.
On the "Just Don't Pay" side, from memory its exactly the same UK & US but both sides are slightly more 'muffled' on the UK copy - which has probably more to do with mastering than mixing.
I bought the UK copy as a new release - loved it and lived it for years.
It was 3-4 years later that I first heard the US copy on a tape, heard the additional few seconds on the intro and was shocked at the clarity!
So, although the UK copy is scarcer the US copy is the one to own to listen to!
Sean