Updated February 2011
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There were many variations to the hasic H-frame design:
The original British design was built as a standard non-folding H-frame design from 1968. In 1971 a folding version was produced with the distinctive frame hinge. The design was definitely over-engineered and is not a quick-fold design for multi-mode commuters jumping on and off buses and trains.
The New-Zealand built Raleigh Twenties had 3 major frame variations. The main difference from the Nottingham design was the lack of the bracing struts to the bottom bracket, and the main tube was a slightly smaller diameter: Most Raleigh Twentys from New Zealand were of the non-folding variety, but there were some folding versions made and here is the first photo that I have seen to confirm it:
There is also another variation which I would rather describe as a "separating frame" version.
Click here to see Mike Toohey's separating raleigh twenty