The several websites I checked show an out of stock note in place of the buy buttons, with no other explanation given.
A spokesperson for B&N said: “Nook Simple Touch and Nook Simple Touch GlowLight will be available in the UK beginning in late October, in plenty of time for the Christmas shopping season. Barnes & Noble's award-winning E Ink products will be available in leading retailers as well as www.nook.co.uk.”
The Nook UK launch had originally been planned for the fifteenth, but thanks to this delay UK reades will be able to buy the Kindle Paperwhite before they can buy the Nook. B&N is also going to have egg on their face because their ex-fiance Waterstones will also have the Kindle in store before the Nook will be available.