Is there a difference between US Worcestershire sauce and UK Worcestershire sauce?
There is some difference between the flavor, but seeing as there are so many other predominant flavors in Worcestershire sauce and that fact that you're (hopefully) not drinking it straight, it's fairly insignificant. It's very common for one product produced in different countries to have a range of manufacturing differences, sometimes arbitrary, sometimes to suit the local palate, and sometimes because of costs, hence people calling American Lea &amp; Perrins a "knockoff."

I've had both, and can assure you that once you've mixed it into a casserole or marinade you won't really miss anything. If you're striving for needlessly authentic British flavor you could always add a little malt vinegar to whatever you're cooking!