The main programme for Post and Go machines in 2014 is on this post.
The Union Flag stamp was not originally
intended to be provided from the Back-Office machines (B1 & B2).
However as these machines are new, showing a new datastring, Royal Mail
have made the Union Flag available from machine B2.
I don't know whether this will be on all four days.
According to the Postagelabelsuk blog
new 'Series B' machines will be in use in 2014, starting at Stampex.
These will be taller and have improved capabilities. The datastring
B indicating series B, and A001 being the
machine number. Machines A002, A003, and A004 will be the self-service
machines at Stampex.
ROC ~ Twin Pigeons ATM Labels - Republic of China (Taiwan) Twin Pigeons ATM labels with machine code 077, releasesd on December 15, 2008 from Taipei Shihlin post office.