Thanks guys, I found some info in the
Kindle help pages on amazon.co.uk. According to that the update is supposed to be delivered automatically via Wi-Fi when you 'Sync and Check for Items'.
It mentions that you already have the latest software if your Kindle is running version 3.3 or later, and that you should update if you have version 3.1 or earlier. Nothing is said about 3.2.1 though..... I can only presume that as mine is a refurbished Kindle, this is some kind of internal updated software Amazon ran on refurbished units prior to the latest 3.3 software? I know it's been mentioned as the version on special offers Kindles, but there are no special offers Kindles here in the UK?