Just as Licquorice was saying, from 35% to ~75% in the 1970s, surprisingly a further increase in the 1980s. I suspect that’s to do with poverty in the 70s though; the 1980s was the era of working class to middle class aspiration and increased affluence, do you think that’s fair?
I’d be interested to see the earlier decades before 1970. I can ask Janet’s mum - who is 95 - about her ideas regarding telephone ownership. My uncle, mum’s brother, had a party line, as did Janet’s folks at their cottage in the woods in Staffordshire. My parents had a normal non-shared landline in the 1960s at the farm.