The Queen was almost killed by a teenager in an assassination attempt later covered up by New Zealand authorities, a former police officer has claimed.

Retired Dunedin detective Tom Lewis says an attempt on the monarch’s life was made when she visited the city in October 1981.

The former officer told the Stuff website that 17-year-old Christopher John Lewis narrowly missed the head-of-state when he fired shots the royal motorcade.

But he claimed police and government officials covered up the would-be assassin’s actions due to fears the Queen would refuse to visit the country in future.

Many in attendance at the event had heard the gunshots, although authorities maintained at the time it was the sound of a council sign falling over.

"You will never get a true file on that, it was reactivated, regurgitated, bits pulled off it, other false bits put on it,” Mr Lewis said. “They were in damage control so many times."

Christopher Lewis later told investigators that he was ordered to kill the Queen by a mysterious Englishman called “Snowman”.

The teenager believed pro-Nazi, far-right groups were “sprouting up” across New Zealand and wanted to lead a local terror cell.

Police files show Lewis had led officers to a fifth story toilet in a building overlooking the Queen’s route after being questioned over a non-related burglary incident.

There, they found a .22 calibre rifle and empty shell casings.

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Despite the apparent attempt on the Queen’s life, the boy was only two charged with two offences – one of possessing a firearm in a public place and a second of discharging it.

He was later jailed for three years and was transferred to a psychiatric hospital in 1983, where he made plans to murder Prince Charles during another royal visit to New Zealand.

Lewis spent much of his adult life in and out of prison and in 1996 was charged with the murder of mother-of-three Tania Furlan, a crime of which DNA evidence later cleared him.