Not only were the stamps counterfeit,but also the booklet covers. As forgeries go, compared to the previous 24p these are said to be produced to a high standard, even down to the perforations. The elliptical perfs however tend to be a bit rough and slope slightly to the right.
The booklet covers did not have the sealing glue spot as someone pointed out. They were 2mm wider than the genuine booklets 50mm compared to 48mm, they were also printed on a thinner inferior card. The inner page is shiny rather than matt on genuine copies.
Many thanks go to Douglas Myall, who sent me a three page pdf document extracted form his complete Machin Handbook CD. These three pages describe every aspect of these stamps and covers (of which there are to many to reproduce here) they also mention other Machin forgeries.
I keep promising my self to purchase his handbook in CD form, maybe I will treat my self on my birthday.