How can it takes only one week in a different country? Sounds weird, or maybe they're being printed in the US?
"The UK will roll out new "iconic" blue passports for a post-Brexit Britain in March — but they will be produced in Poland by a French-Dutch company."
(The UK "blue" is basically black, whereas US passports are actually blue)
https://py.usembassy.gov/wp-content/uploads/sites/274/2017/0...
Though even postal items can arrive in a week as well, with luck.