One of the queen's senior guards has been filmed sniffing a powder-like substance off a sword while on duty in St James' Palace.

Footage obtained by The Sun shows Major James Coleby, 41, snorting the substance off a ceremonial sword while commanding a unit that responds to royal security breaches.

The video shows another officer, 27, preparing a line of the powder onto the sword with a plastic card.

He asks Major Coleby: “How much? Two inches? You want two inches of that? If you get rid of that I’ll be mightily impressed.”

Major Coleby then bends over the blade and snorts the substance. As he does so a woman can be heard shouting: "Don't do it, for the love of God!"

The high-profile guard, who is a veteran of the conflicts in Iraq and Afghanistan, was in charge of 15 men at the time the video was filmed.

The Ministry of Defence has launched an investigation into the incident, confirming that Army personnel who do not comply to the "high standards" are subject to discipline.

An MoD spokesperson told The Independent: “The Army expects all personnel to stick to its high standards and any found to fall short are disciplined robustly. An investigation is underway.”

Colonel Richard Kemp, a retired British Army officer who led troops in Afghanistan, described the behaviour as "embarassing", but said he thought the substance was unlikely to be drugs.

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He told The Sun: "This behaviour is both highly worrying and acutely embarrassing for the British Army. However, I’d be very surprised if this powder does turn out to be drugs.

"Even if it’s officers larking around, they would still be given a very serious talking-to. They are there to set an example and impose discipline."