The low value Machin stamps - 1p, 2p, 5p, 10p & 20p - will change from sheets of 200 with water-activated gum to sheets of 25* self-adhesive. (*I suspect this means counter sheets of 25 but philatelic sheets of 50 with a gutter.). These will have security slits but no iridescent security overprint. The smaller sheets, which are more convenient for post office use, will be introduced operationally as needed, and there will be no official first day of issue, but the first day of philatelic availability will be 8 March 2011. Normally gummed sheets will continue to be on sale from the Philatelic Bureau at Tallents House until further notice.
The new Country Definitives for England, Scotland, Wales and Northern Ireland, to be issued at the end of March, will also be printed in sheets of 25 but will have conventional water-activated gum. Values are expected to be 76p & £1.10. Apparently the low usage of these does not make security features an economic proposition. The new printings will be in litho by Cartor, changing from De La Rue gravure printings.
The Machin definitives required for the April tariff change will be self-adhesive with iridescent overprint in sheets of 25. These should have the M11L year code and source code MAIL. Values are expected to be 68p, 76p, £1.10 & £1.65. All Machin printings are expected to be by De La Rue in gravure.
No date of issue for tariff change stamps has yet been announced.