Navel oranges have been around for a better part of two centuries, the 70s predate the debut of my higher consciousness, but I'm sure British people had any fruit before 1983. Before that any 'orange' was a lump of wood coated with a virulent orange paint made from lead and dioxin. They are the 'winter orange' and Valencia the summer, though as they're not tied to geography any more, you can get both in any season. Google says they were discovered in 1820 in Brazil.
I don't think the aborted orange has anything to do with the infertility, but it may be a result of the same mutation, which prevents pollen production. No pollen, no fertilization, no seeds. They can be fertilized by other varieties of oranges so it's possible to get occasional ones with seeds. As they can't reproduce sexually, every navel orange is a clone of the original (as such there's a lack of genetic diversity). Kind of like bananas (though they're sterile because they're triploid rather than a mutation). I think seedless grapes came from a mutation.