Engadget reports that they received word that at 1:30pm today O2 will launch a new 16GB iPhone in the UK.

Update:
The Apple store sells now 16GB iPhones and 32GB iPod touch.

Currently only 8GB Apple iPhones have been available. O2 just recently streamlined its tariffs and now apparently offers an iPhone with more storage that has a price of £329 (~$647). The currently available 8GB iPhone sells for £269 (~$) in the UK.
I am a bit surprised that the UK would get the 16GB iPhone before the United States, but maybe there will be a surprise release of the 16GB in the U.S. today too.
More details on Engadget.