81-year-old Flannery was one of the last people to have talked to 'Beatles' founder shortly before he was killed in December 1980, reported Daily Express.
Flannery used to handle the band's bookings. His book contains insights into the state of mind of Lennon shortly before he was murdered in the lobby of the New York apartment where he lived with his wife Yoko Ono.
"We enjoyed a lengthy conversation. We talked a lot of rubbish of course. He was very well and happy but he missed Liverpool, he missed the others and he missed London but he told me at one stage that he regretted 'getting too political'," Flannery said.
Flannery said Lennon believed that his thoughts on peace and lyrical barbs had made him a government target.
Lennon was killed at the age of 40.