I thought you would like to have a look at this Greetings Retail Booklet. It was issued on 13 May 2008. Consisting of 2 x 1st. class 'Ice Cream' stamps which look good enough to lick ( as issued last year for the Beside the Seaside set ) and 4 x 1st. class gold Machin definitives.
All the stamps in the booklet are self-adhesive. Printed by Walsall Security Printers in Gravure on OFNP/SA paper.
Note the Ice Cream stamps issued last year were in sheet form and did not have self adhesive gum, so I guess some people did actually lick them.