Thanks go to David Alderfer who sent me this information below, David, is a long estabished friend of Larry's and a well known philatelic author. He resides in the Chicagoland area, U.S.A
Here is some additional information about the first (1974) self-adhesives. I believe it originated in a Rushstamps sales list from several years ago.
“These original self-adhesives were the brainchild of two philatelic entrepreneurs -- Mr Derek Worboys and Mr John Daynes who both submitted orders for these Machin octagonal diestamped designs to Her Majesty’s Stationery Office to be produced on self-adhesive paper. These stamps were produced in late 1973 just prior to this special service being withdrawn. The 1st Series was duly issued on February 10th which was the exact date of the 10th Anniversary of the sierra Leone self-adhesive Issue.” (note): Sierra Leone was the first country in the world to issue self-adhesive stamps and did so in 1964.)
The Rushstamps listing continues: “These self-adhesive [the G.B. Machin versions] are officially approved by the Post Office and remain fully postally valid and are an important part of British post history.”
Rushstamps notes the early Machin self-adhesives exist in three series. Series 1 by Worboys has the Machin value printed on square, self-adhesive paper with rounded corners. Series 1 consists of five values -- ½p (light blue), 1p (crimson or maroon), 1½p (grey-black), 5½p (a se-tenant 5p light violet value with a ½p light blue) and 8p (a se-tenant 5p with 3p (I do not have an example of this value and cannot provide the colors.]
Here is a scan of the one penny value from Series 1 (square).
These five values of Series 1 were offered by Rushstamps several years ago at £150 and a used set, noted as “scarce,” at £125.
Series 2, also by Worboys, consists of only one value, a 3½p (grey-green). This value included a special slogan inscribed “You just cannot lick self-adhesive stamps for speed and hygiene.”
Royal Mail took offense at the slogan which implied that licking a stamp might be harmful to the mailer’s health and required that it be overprinted in red with “This slogan embarrasses the British Post Office and must be detached before use.” The overprinted version was offered by Rushstamps for £15.
Rushstamps notes “A 3p value . . . Also exits and is very rare (with or without overprint) each . . . . . . £125.00.”
Series 3 was produced by John Daynes. There were nine values The additional values not included in the 1st Series were 2p (green), 3p (dark blue), 3½p (grey-green), and 4p (ochre).
This set had the stamps printed on circular paper and is listed in the Rosen Catalogue, which I’ve heard of but have never seen or used.
Rushstamps offered this set for £350 and a used set at £295.
According to the advertisement for these stamped-to-order self-adhesive labels there were 1,000 sets of Series 1 and Series 3 produced. No total is given for the “cannot lick” single value.
In an ad that appeared in the May 28, 1979, issue of Linn’s Stamp News Gustamps of Brighton (limited web site at http://gustamps.net/) offered five values from ½p to 3½p with two gum varieties and one additional paper variety. It is not possible to discern from the wording of the ad whether the self-adhesives were from Series 1 or Series 3 or both. The offer for eight different stamps was $125.
Back to the Rushstamps offer. There is the comment about the Series 2 3p stamp without the offensive slogan that “only a few sheets of 12 known.” This comment speaks to Roy’s question in the original post where he says: “I had never (until today) come across a complete sheet or part sheet. This (shown below) is a sheet of 12, the block is showing multiples of the 2p value. It is currently up for sale at £999. Judging by the rounded corners it looks as though it is a whole sheet. Can anyone confirm how many of these stamps were printed in one sheet?”
The Rushstamps ad concludes with this comment: “Large Rectangular Self-Adhesives also exist and are very rare. Ask for details.” I do not know what these rare, large rectangular self-adhesives are.
These first British self-adhesives, privately produced but postally valid, were early on in their life somewhat pricey. Demand for them increased after Royal Mail introduced in October 1993 because they were seen as pre-cursors to the official Royal Mail experimental NVI versions in horizontal format issued that year.
Myall in the Deegam Handbook in Appendix 6, pages 17-19, records the early STO gummed labels.