Bradbury and Wilkinson were the printers of the first Machin high values in 1969, these were the recess printed pre decimal stamps. The set consisted of 4 values , 2/6d , 5/- , 10/- , and £1. None of the stamps had phosphor bands. the pre decimal issues are shown below.
The decimal series followed in 1970 (in fact issued 3 or 4 months before decimalisation).
Similar in design but but with 10p, 20p, 50, and £1 values.
The 10p was printed on phosphor Coated Paper, so were some of the 50p values.
These were also printed on two types of paper, one dull, one bright.
Due to shortages of the original papers the printers used their own paper, this is termed in catalogues contractors paper, the original refered to as post office paper.
The layout of the sheets also changed, on the decimal issues this gave rise to a variant of the one pound value. The first printings of the £1 value had thick horizontal lines of shading, and the reprint had vertical lines, known to specialists as cross hatch of the printing design, the difference in the printing layout and finish can only be seen with a good magnifying glass.
This variant should be checked on the pre decimal script £1 value as there are two distinct types.
In 1972 the value tablet on the £1 value was also changed from a script type to a more modern
block type (see picture left to compare) which gives a 3rd variant.
During 1977 things started to get exciting in the stamp world, a brand new set of high value stamps were introduced, printed in photogravure. These were of a large vertical format similar to the commemoratives of the day. They were also available in gutter pairs, which was also a first for stamps of high value. There are several values to collect from this series ranging from £1 to £5.
High values then reverted to the castles stamps for a short time (these were not Machins).
Small format :
After the castles issues of which there were several printings, high values reverted back to the Machin design, to that of the small format of today, the reason for the change , quote "the post office needed to bring in some sort of uniformity in the size". Enschede of the Ntherlands were the chosen printers.
This issue of high value Machins then changed again dramatically they were still in the small format but were re-engraved and more security features were added. These were as stated were printed by Enschede, but then the contract reverted to De la Rue. These are the current HV stamps on sale at this time.
The cut off point for high value stamps changed in 2003 to that of £1.50p. All stamps below this value are now classed as a normal low value, which makes for confusion to the layman as this includes the previous £1.00 issued before hand.
A new £1 Ruby Machin is to be issued in June 2007 to celebrate the 40th anniversary of the Machin design. This will not be classed as a high value.