A British man has pleaded not guilty to charges over an alleged plot to assassinate presumptive Republican nominee Donald Trump with a police officer’s gun at a Nevada rally.

Michael Steven Sandford, 20, faces up to 30 years in prison if convicted of federal charges of disruption of an official function and two counts of firearm possession, according to the Associated Press.

A grand jury indicted the English-born Mr Sandford, who previously told the court that he drove to Las Vegas from California to kill the New York business tycoon. He was arrested at an event at the Treasure Island hotel-casino on 18 June.

Mr Sandford’s mother has told court researchers that the defendant mental health troubles, such as obsessive compulsive disorder, and had also previously suffered from anorexia.

A magistrate judge questioned Mr Sandford’s competency to stand trial at a hearing on 20 June, but a federally appointed public defender said that he was fit to take the stand.

The US Secret Service said Mr Sandford told police he had planned to kill Mr Trump for more than a year, during which time he lived in Hoboken, New Jersey, where he reportedly overstayed his visa and was living out of his car.

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Mr Sandford’s father said his son had lived in New Jersey for 18 months. He then drove across the country to California.

The 20-year-old was reported to have been at a Battlefield Vegas shooting range the night before the alleged assassination attempt, firing off some 20 rounds from a Glock 9mm pistol.

Security was tight at the 18 June rally, as attendees had to travel through metal detectors upon entrance.

Mr Trump had reportedly complained that the tight security – run by the Secret Service, Las Vegas police and the casino – had prevented some people from seeing him speak.

“I’m not happy about it, but I have to put up with it,” Mr Trump said in his speech. “They didn’t bring enough machines.”

The Secret Service said that Mr Sandford had another ticket to a Trump rally in Arizona later that day.