Royal Mail have announced that this booklet will be issued at Stampex alongside the Seaside Architecture set and miniature sheet (and the day after the Symbolic Flowers Faststamps!). The Sustainable Fish retail booklet issued 18 August will be distributed by Tallents House on the same date.
Two sponsored postmarks have been announced so far for this booklet and are shown below. The booklet contains 2 x 1st Locos of Wales stamps (LMS No. 7720 leaves the Britannia Bridge with a Bangor-to-Holyhead local train c.1930) and 4 x 1st class Machin definitives. These will have source code MCIL but we cannot be sure which year code they will have. The Football Heroes 2 booklet issued 2 days after the Locos miniature sheet had M13L but that was printed last year with Football Heroes 1.
13186 Smethwick is available from the Midland Special Handstamp Centre, and
13222 Cardiff is available from the Wales and West Special Handstamp Centre.
UPDATE 29 AUGUST: Cylinder booklets show fewer numbers than I would have expected:
Starting from left, above 'GE', they are iridescent, phosphor, red, black and gold. But whereas the stamp is clearly monochrome black and white, the selvedge is rather more olive-grey in colour, suggesting printing by four-colour process as usual. (It has been pointed out to me that this applies to all the Locomotives booklets - it's taken me until number 4 to notice!)
The old 0845 telephone numbers are on the booklet cover, confirming that these were printed at the beginning of the year, as confirmed by the packing date on the wrapper: