The Duke of Sussex’s US visa application should remain private despite him admitting taking drugs in his memoir, a judge has ruled.

Harry’s reference to taking cocaine, marijuana and psychedelic mushrooms in his book Spare prompted a conservative Washington DC think tank to question why he was allowed into the US in 2020.

In his ruling seen in court documents on Monday, US judge Carl Nichols said “the public does not have a strong interest in disclosure of the duke’s immigration records”.

His judgment added: “Like any foreign national, the duke has a legitimate privacy interest in his immigration status.

“And the duke’s public statements about his travel and drug use did not disclose, and therefore did not eliminate his interest in keeping private, specific information regarding his immigration status, applications, or other materials.”

The Heritage Foundation brought the lawsuit against the Department for Homeland Security (DHS) after a Freedom of Information Act request was rejected, with the think tank claiming it was of “immense public interest”.

Judge Nichols went on to say the public’s interest in disclosure of Harry’s immigration records is “outweighed by the duke’s privacy interest”.

He said: “Public disclosure of records about a single admission of a foreign national in the circumstances described above would provide the public, at best, limited information about the department’s general policy in admitting aliens.

“And the marginal public benefit of knowing that limited information is outweighed by the privacy interest the duke retains in his immigration status and records.”

Some of the judgment has been redacted – in particular facts the duke has not disclosed publicly in relation to his immigration status and records, and what was contained in his visa application.

Much like health, financial, or employment information, a person’s immigration information is private personal information

In his controversial memoir, the duke said cocaine “didn’t do anything for me”, adding: “Marijuana is different, that actually really did help me.”

The Heritage Foundation’s lawsuit argued that US law “generally renders such a person inadmissible for entry” to the country.

The think tank also said answers on the duke’s prior drug use in his visa application should have been disclosed as they could raise questions over the US government’s integrity.

In the DHS’s response to the legal claim, it said: “Much like health, financial, or employment information, a person’s immigration information is private personal information.”

The submissions made by lawyer John Bardo on behalf of DHS also said no “publicly available information, shows that Prince Harry was ever convicted for a drug-related offence”.

Mr Bardo added that any suggestion from the Heritage Foundation of wrongdoing on behalf of the US government was “purely speculative”.