Rumour has it that the US release date for the Wii U will be the week before Black Friday, that's the 19th to the 23rd of November. The source of this information is GoNintendo, having heard this themselves from a US employee of GameStop.
Nintendo of course will not confirm this, but as Black Friday is the busiest shopping day of the year in the US, it makes sense. In the past Nintendo have been worried about releasing before Xmas due to hardware supply issues. However this is 2012 not 2007 and the demand for gaming hardware has dropped off considerably.
One issue with releasing the Wii U on Black Friday is that this is part of the Xmas shopping season. Nintendo don't want these consoles sitting in their boxes until Xmas day, they want people playing them and raving about how good they are, creating more sales. Releasing a couple of weeks before could be the best strategy.
As for the UK release date, there's nothing concrete yet. All we know from Nintendo is they intend to launch the Wii U in the UK this year. There are rumours about hardware issues with the Wii U GamePad, which could push the release date back to December 2012.