Britain used to have "Ordinary level" (O levels) at age ~16 and "Advanced level" exams (A levels) at ~18. Students usually studied 5-8 O levels and then either left school to pursue a career or went on to study (usually) 3 A levels and go to university.
O levels got replaced back in the 80's. A levels never got renamed.
This was certainly the case in most of Britain. Scotland has a separate education system from England and has today and historically offered different high school level qualifications ("Highers" etc).
Sorry, yes, my bad. Thank your for the correction