The British army said on Tuesday it had launched an investigation after reports that a man who was pretending to be a priest spent a night at a barracks with soldiers tasked with protecting Queen Elizabeth near her Windsor Castle home.
The Sun newspaper reported that the imposter was allowed onto the barracks of the Coldstream Guards without showing any credentials or identifiable documents and later ate, drank and shared stories with soldiers.
The queen was not in Windsor during the incident which took place last Wednesday, the paper said.
"The army takes this breach of security extremely seriously and it will be thoroughly investigated as a matter of priority,” a Ministry of Defence spokesperson said. "This incident is now part of an ongoing investigation and would be therefore inappropriate to comment further at this time."
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The Coldstream Guards are a serving infantry regiment in the British Army whose responsibilities include the ceremonial role of protecting royal palaces.
The queen returned from a short break at her Sandringham home in eastern England last Wednesday but Buckingham Palace said the monarch was not present at Windsor at 0820 GMT, the reported time the man was escorted from the barracks.
A palace spokesman said the incident was a matter for the defence ministry.
The Sun said the man had claimed to be a priest and told officers he was a friend of a member of the battalion's chaplain.
He was then invited in and had something to eat and drink and proceeded to tell lots of "tall stories", the newspaper said citing a source.
Suspicion about his identity began to be raised when he "started talking about how he had worked as an ejector-seat test pilot and had some organs replaced" the source told the Sun.