I have had a e-mail from Ian Billings informing me of a change to the background code of the Large 1st and 2nd class stamps from booklets of four.
At the same time via comment Ian Price has confirmed this change.
"I have just obtained copies of these new booklets & noticed another change not mentioned in the base note. The position of the 'F' code has changed. It is now 'MFIL' in the third wavy line, instead of 'FOYAL' in the second wavy line"
Ian price also mentions a change to the security slits on the self adhesives obtainable from stamps from the Prestige booklet.
"The security cutouts on the Machins in the panes in my 2 copies of the PSB appear to be a new version. The top loop is uninterrupted (type 1) & the bottom loop is interrupted (type 2). This is the same for all of the stamps."
Thanks go to both Ian's for these reports.