Complex sentence: The repercussions of the affair severely damaged Macmillan's confidence; he resigned as prime minister on health grounds in October 1963, and his party was defeated by Labour in the 1964 general election.
Split into simpler sentences: The repercussions of the affair severely damaged Macmillan's confidence, and he resigned as prime minister on health grounds in October 1963. His Conservative party was marked by the scandal, and was defeated by Labour in the 1964 general election.