From all the stories I've heard from all my professors (some are relatively young) and a lot of grad students, phD's last between 4-5 years in the US. 6 is not as common. The first year you usually take classes and TA a freshman lab. Then, in 2nd year, you take what are called you "cums" or cumulative exams. Sometimes your 3rd semester is spent taking classes, but by the 4th semester you usually have picked a lab group to join. They are generally easy to pass, and the grade you get usually doesn't mean anything so I hear (its more like pass/fail). It's basically a way for the professors in your department to make sure you aren't retarded. My professor told me that one of his professors put questions that HE didn't even know the answer too, and that he was working on, to see if randomly one of the new phD students could answer it. My prof told me, some professors like to make it easy, some like to make it ridiculously hard, but I'd say easy is the most common. I don't think people fail their cumulatives, you also get like 2 or 3 tries per test to pass. This is all second hand info, I'm just resaying what has already been said. If you're in the UK, is there not a single U.S. professor in your school? Or in a nearby one?