How come they have an American high school graduation when the programme is set in Britain?

In the graduation 일 episode the characters have an American High School style graduation with diplomas and a valedictorian. However the it is supposedly set in Britain where this doesn't happen and 당신 don't get diplomas when 당신 leave high school and don't need credits to graduate, 당신 just leave school with whatever GCSEs 또는 A levels 당신 sat.