In Brief:

It is the Beatles, that can take partial credit for the coming about of the Hells Angels Motorcycle Club, London.
From the mid sixties onwards the Hells Angels Motorcycle Club in California started to become world famous, spawning many imitators, especially in England.

Now there was a problem; as the Hells Angels Motorcycle Club is but one club, and not a term for bike enthusiasts in general, as the media would have people believe. With San Francisco being about 8000 miles from London, the solution was to start a chapter in London. Eventually, two people went from London to California and joined the club after "prospecting" first. Two charters were issued on July 30th, 1969. One to South London and the other to East London. In 1973 the two charters came together as one, simply called London.