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English said that after 27 years in parliament he decided during his summer vacation that he wanted a break from politics.
"This is more about myself and my family having spent most of my adult life, all of their lives, with the demands of politics," the 56-year-old told reporters.
"I want the opportunity to start again on a different life."
A staunchly Catholic conservative, English served as prime minister for just under a year before being replaced by centre-left leader Jacinda Ardern in October last year.