Complex sentence: The pattern, however, is not replicated among the thirteen post-World-War-II prime ministers of Great Britain, only two of whom, David Cameron and James Callaghan, have been left-handed.
Split into simpler sentences: The pattern, however, is not replicated among the thirteen post-World-War-II prime ministers of Great Britain. Only two prime ministers after World War II, David Cameron and James Callaghan, have been left-handed.