With regard to the US:
See
here for on interesting stat.
See
here for another.
So, between 20m and 60m US citizens have a passport ... and it is well known that 90% (ick) of Americans never leave their country.
It wouldn't surpise me if the UK figure was 60-70% people who have a passport, given that many young 'uns have yet to get one, there are probably some who never will, a significant underclass of people who don't want one and older people who have let their lapse ...
As for the UK statistics, the number per year could be swollen by the need for biometrics, immigrations, people who renew less than the 10 year duration, lost passports ... etc. I'd hazard therefore that multiplying the number per year in one year by ten is unscientific.