From Nook Press:
We are writing to announce an important change to our NOOK Service that will affect NOOK Press vendors publishing content in the United Kingdom. Effective March 15, 2016, NOOK will no longer sell digital content in the United Kingdom. The NOOK Store on NOOK devices sold in the UK, on the NOOK Reading App for Android, and at www.nook.com/gb will discontinue operations.
. . . .
There is no change to NOOK Service or NOOK Press in the United States. If you are an author based outside the US in a supported country, you can continue to use NOOK Press to publish digital content in the United States and receive payment in your local currency.
Link to the rest at Nook Press and thanks to Joshua and others for the tip.