An undercover policeman posing as a criminal entered a British Army base where he was invited into the armoury to see live rifles, a court has heard.

Coldstream Guards Regimental Sergeant Major Kirtland Gill, 41, and Lance Sergeant Rajon Graham, 33, allegedly plotted to sell hundreds of bullets to the officer, “D”, for cash.

Southwark Crown Court heard Graham took D to Victoria Barracks, near Windsor Castle, where the regiment, known for its red jackets and black bearskin hats, is based, on December 17 last year.

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The Coldstream Guards is the oldest continuously serving regiment in the British Army and is responsible for protecting the Queen.

“When we entered the camp, he had obviously spoken to the guards at that point,” the officer said, giving evidence from behind a screen on Tuesday.

“I was nervous of being on a military camp in the way I was portraying myself as a criminal.”

D said they parked on the parade square, while waiting for Graham’s friend, who he said was being interviewed by The Sun newspaper.

The court has heard Gill was interviewed because he was the first black regimental sergeant major in the Household Division, which guards Buckingham Palace and Windsor Castle.

The undercover officer told jurors he said to Graham, who he knew as “Solj”, he thought it was “too hot” or “too risky” for him to be on the base.

“He kept saying it was fine, I was with him and while I was with him everything would be OK,” he said.

“Shortly after he was saying I could go with him into the armoury to view the rifles.”

But asked by prosecutor Duncan Atkinson QC if he took Graham up on the offer, D said: “No. I decided that was a bad idea.

“It was a challenge to go into the Army base but to go into the armoury with live weapons with whom I perceived to be a serious criminal was not a risk I was willing to take.”

Graham is then said to have driven “D” to Gill’s nearby home to collect a batch of ammunition, which he bought for £1,000.

The court heard Graham sold a total of 300 9mm bullets, which he called “sweets”, wrapped in Bacofoil bags, for £5,800 in cash.

He is not standing trial, having previously pleaded guilty to four counts of selling ammunition between December 7 2020 and January 28 2021.

Gill, who joined the Army in 2001, denies conspiracy to sell or transfer ammunition between December 2 2020 and January 30 2021 and possession of a prohibited weapon.