We have already reported that the new M12L printing of the 2nd class Machin stamp is printed by Walsall Security Print, rather than De La Rue (who have probably been busy printing new airmail rate stamps). Now we have a suggestion that the Diamond Jubilee 1st class stamp in Business Sheets - issued only on 6 February this year printed by De La Rue - has now been printed by Walsall!
The gap in the security cuts is clearly different. We don't yet know the printing date on the Walsall printing.
This is the Walsall-printed retail booklet of 12, with code MTND referred to by Anonymous in the comments.