Here is a rundown of the text sent by Roger extracted from a photo copy from a Dealer.
A MACHIN MYSTERY
In early to mid 1994 a mystery Machin 2nd class stamp appeared. These stamps looked very noticeably different. The colour is very much richer and the surface shinier, similar to PCP2. They are also printed on a different paper and the gum is almost invisible with a matt finish, a type of gum not previously used on any British stamp.
A new type of phosphor has also been used, the stamps appearing to be missing the phosphor to the naked eye but with a different reaction under the ultra violet lamp. The perforations for the record are the normal elliptical type.
Or a much more comprehensive history of the Machin Mystery we refer you to the February Stanley Gibbons Monthly where there is an article written by John Deering which explains more fully this interesting saga.
I am still not convinced are they forgeries? So do a lot of other people, If you have any more information on this oddity please let us know via the comments dept.