Dark Colours - Inverted watermark printings.
These are usually from booklets, the relative scarcity of the inverted watermark compared to the upright was brought about because although there are equal numbers of both produced for the booklets, many more of the stamps were produced conventionally in sheet form for sale over the counter, and these normally had the watermark upright.
This photo is part of a sheet courtesy of the British Post Office, and it shows why half of the booklets would have the inverted watermark.
1951 - New colours Inverted watermark
illustration showing the stamps with inverted watermarks and a 6d booklet.
Dark Colours - sideways watermark printings
Normally from Coils, to be used in stamp machines, the five low values were produced as required, the ½d in January 1938, the 1d, 1½d and 2d in February 1938, and the 2½d not until June 1940.
A coil leader from the Z type which had 1,920 x 1d stamps. The 1d stamps were affixed to this 'leader' to the coil which was installed in the stamp vending machine.
1951 new colours sideways watermark
Introduction
definitive stamps
Definitive stamps inverted watermarks
High Value stamps
Coil stamps and leaders
Sheet markings
stamps in booklets
Forces Mail and Airletters
Commemorative issues
Overprints
Wartime slogans
