Menzies, who has no command of Chinese, was born in London, England. Early versions of his book erroneously said he was born in China but in actuality he moved to China when he was 3 weeks old. Menzies joined the Royal Navy in 1953 and served in submarines from 1959 to 1970. Menzies claims he sailed the routes sailed by Ferdinand Magellan and Captain James Cook, while he was commander of the diesel submarineHMS ''Rorqual'' between 1968 and 1970, a contention questioned by some of his critics.; see particularly note five of the Appendix.
In 1969 in the Philippines, HMS Rorqual rammed a U.S. Navyminesweeper, the USS ''Endurance,'' which was moored at a pier. This collision punched a hole in USS Endurance but did not damage HMS Rorqual. The ensuing enquiry found Menzies and one of his subordinates responsible for a combination of factors that led to the accident, including the absence of the coxswain (who usually takes the helm in port) who had been replaced by a less experienced crew member, and technical issues with the boat's telegraph. Menzies retired the following year, and stood against Enoch Powell as an independent candidate in Wolverhampton South West during the United Kingdom general election 1970.
Menzies currently resides in North London with his wife Marcella.