Moving to the UK is more complicated than some people realize. It's not like moving to another U.S. state, where you can just pick up and go. There are many difficulties that people aren't prepared for. It’s a common misconception that an American can just pick up and move to the UK just because they’d like to. This is entirely untrue, you need to qualify for a visa to move to the UK! Be sure to do your research before making plans, you may not qualify at all.
Despite the UK being an English speaking country, there ARE cultural differences and these are also relative to the community/region in which you're living, where you work, and your family. You'll practically have to relearn to shop, cook, drive, etc. The easy questions on Who Wants To Be A Millionaire become the hardest because they are purely culturally based. Some expats love it and some find that they hate it. Most go through mild to severe culture shock but some don't. Once people get past the initial "honeymoon" period of excitement and newness, feelings of homesickness, loneliness and frustration can set in. It can be very stressful at times, especially during holidays.