Honestly I just took the present day number of houses in the UK (30 million or so) and divided by the number of pubs in the UK (46,800 or so) which gave 641 houses per pub, then I knocked that down to 300 lest people think I was over-estimating the number of houses.
Of course, that present day number is 30 million houses for 67 million population, i.e. 2.2 people per house - not the 20 people per house from your assumptions.
Of course, that present day number is 30 million houses for 67 million population, i.e. 2.2 people per house - not the 20 people per house from your assumptions.