It could have evolved from imitating the sort of steps that some of the soul groups who visited the UK in the 60s did on stage, as dance routines were the norm for these groups. The "northern dance" has evolved over the years, the way we danced at the Torch was a lot more simple than the way we dance now. (apart from the acrobatics which are less common now, thank gawd!) with less fancy footwork. It's really a development of stepping side to side on the beat, the way you might do when not actually dancing, but just sort of swaying.
Someone once told me that the style came from seeing a dance that Alvin Cash and the Crawlers did on stage whilst on a visit to the UK. The backdrops and the like were certainly part of the US soul group' repertoire, I've seen film of the Flamingoes backdropping and my mate Terry said that when he saw Philip Mitchell in the early 70s he did a few of them.
Tony