Credit where it's due, it was the Australians who came up with the idea. Rex Williams (former snooker and english billiards pro) saw them while visiting Aus and brought the idea back to England in the 1970's I think. Not as popular in British pubs now as they used to be.
You have it backwards. Blackball is a spin off version of American 8 ball. Then spread to the UK and the British put their twist on the game in the early 70's. From there is spread wider to other countries like Australia.
It was around 1970 that the first pool tables began to appear in the UK's pubs.
The game's rapid increase in popularity was due entirely to the availability of the small-sized table which, when installed in pubs, provided a welcome additional source of income for landlords.
In those days there was some experimentation with the table specifications and a variety of coin-operated tables were manufactured for the booming pub scene.
Some designs were more successful and aesthetically pleasing than others, but as time passed a degree of standardisation was achieved.
By the late 1970s the game had become well established throughout the United Kingdom.
Other countries in which it gained rapid acceptance were Ireland, France, South Africa and Australia.
Reflecting its American origin, when first introduced to the United Kingdom pool was played with solid-coloured balls numbered 1 to 7 and striped balls numbered 9 to 15, of the kind shown below.
Such ball sets were referred to as 'spots and stripes' in the UK and they continue to be used in the games of American pool and Chinese Eightball.