It's a tricky question and there are far more practical things to know than current affairs, e.g. customs and taboos, language, currency etc.

For example, I've met people (American and others) who weren't aware that the UK hasn't switched to the euro. I once pointed this out to two surprised Americans on a flight to London - when you are a few hours from landing this is more useful than knowing the prime minister's name!

Beyond knowledge and ignorance (there are certainly ignorant Brits too) there may be a difference in attitude which sometimes comes across as ignorance. I'm relocating from London to NYC in just over a week so it will be interesting to experience the differences, I've heard that despite being quite cosmopolitan NYC is generally a little more inward looking.