As explained on the reverse of the pack, the 'Service Indicia' which was previously printed on plain white labels is now printed on Post and Go stamps (or Faststamps).
These stamps (with the same values) are readily available at Post Office branches with the NCR self-service machines, the number of which will increase from the current 225 (mix of old and new machines) to over 700 by the end of 2015.
The stamps in the pack have a different datastring to those from the machines, however, and don't even mimic the 'live' versions which have kiosk numbers 67 upwards. These have a datastring similar to that in IAR and previous exhibition machines and so unlike those from either the Wincor-Nixdorf or NCR machines.
B7GB14 C001-1840-015This indicates: Reel B, Month 7, Great Britain, Year 14, Machine C001*
The 1840 is supposed to be the session number and 015 indicates the pack number (this is the 15th Post and Go presentation pack).
The pack doesn't explain the VAT codes which are (in sequence as shown) E4 B4 F4 C4 and H4.
* The July Philatelic Bulletin quotes this as C002 but that is wrong. Also, both brown and blue stamps show Reel B. If nothing else this shows that they are not printed together, but in two very separate major print runs.
Royal Mail are not producing first day covers of these stamps.
One good thing to come from this is that Tallents House are using up old stocks of base stamps, the blue stamps being coded MA12, and the brown undated!
A reminder of what a other datastrings looks like Wincor (top), machine NCR (centre) compared with ones from the pack: