Stalker allowed to stroll into palace grounds, just 250m away from Queen Elizabeth II

Queen Elizabeth II attends a ceremony to mark her official birthday at Windsor Castle on June 13, 2020 in Windsor, England. Photo / Getty Images

A security blunder reportedly saw a stalker claiming to be a priest allowed inside Victoria Barracks, just metres away from Windsor Castle.

The Sun reports that the soldiers at the barracks were approached by a man claiming to be a priest and a friend of the padre to the Coldstream Guards at the base.

The man did not show any identification or any credentials but was allowed to spend the night eating and drinking in the Officer's Mess.

He reportedly spent the night drinking with senior officers and telling tales about having served in Iraq.

The man was then offered a bed for the night.

The alarm was only raised in the morning after the man had had breakfast in the premises, The Sun reports.

Queen Elizabeth II attends a ceremony to mark her official birthday at Windsor Castle on June 13, 2020 in Windsor, England. Photo / Getty Images

Police were called and escorted the man, found to be a "fantasist", away from the premises.

The UK Ministry of Defence has launched an urgent investigation into the alleged security breach.

The man spent nearly 16 hours about 250m away from Windsor Castle.

The Queen, who had spent Easter at Sandringham, returned to the castle just two hours after the man was escorted out.

"This is just an extraordinary breach of security," a source told The Sun.

"The guy turned up at the gate in the evening and said his name was Father Cruise and claimed to be a friend of the battalion's Padre Rev Matt Coles.

"He was invited in and offered something to eat in the Officer's Mess," the source added.

The security breach comes as William and Kate plan to move to Windsor full-time and take up residence at Adelaide Cottage in the grounds.

According to TalkTV, quoted by The Sun, the man is known to local authorities and has not been arrested.