Raleigh thought it might save a few bob by making a version of the Mini without front suspension. In so doing they disregarded the fact that one of the purposes of the suspension was to limit the forces applied to the frame. The frames without front suspension were therefore subjected to higher forces than they were designed to withstand, and on some the main beam/steer tube joint fractured as a result.
Raleigh's solution was to provide a steel 'clamshell' to strengthen the joint. It consisted of two pressed steel plates, shaped to fit the frame, that were bolted together over the joint. The clamshells were black, bulky and heavy. They also had a kind of 'Starsky and Hutch' stripe for a sporty appearance.
The bikes without front suspension, having a bumpy ride and being prone to fracture, are obviously less desirable than those that do have it. You can identify them by the absence of the rubber bellows just above the front wheel. The clamshell bracket, where fitted, is instantly recognisable. You can find out more about the small Moultons, and other old bikes as well, at the wonderful Bicycle Hub website.