UK Sherlock fans: help!

[lady_ganesh]

Are there indications in the show about what class John might have come from? I'm toying with Harry being successful in tech and overcoming her social station, or, alternately, John being the one who rebels from his upper-crust background by running off and joining the military.

Help the tone-deaf American?

EDIT: Just running into say I love using my 'flist knows all' tag because IT'S TRUE.