Good stuff, this 'Google' thing
It
is but there's no guarantee that what comes out of it is correct or complete.
In particular, the article that you cite fails to point out that in the UK the quadrantal rule and semicircular rule apply only to
IFR flight
outside controlled aispace. That makes the semicircular rule a bit redundant. VFR flights are
advised to adopt quadrantal levels.
Outside the UK, the quadrantal rule is virtually non-existent, and a different flavour of semicircular rule, intended primarily to separate IFR from VFR, exists for both controlled and uncontrolled airspace.