This video shows the dramatic moment a soldier from the Queen's Guard turned his rifle on a tourist who grabbed him outside Windsor Castle.

Friends are heard giggling as the Asian man marches alongside the serviceman - who is thought to be from the Scots Guards regiment - and rests his hand on the soldier's shoulder.

But the grin is soon wiped off the tourist's face as the soldier suddenly points his weapon directly at the man, barking: 'Get back from the Queen's Guard!'

On patrol: A soldier from the Queen's Guard marches outside Windsor Castle as a tourist follows him

Touchy: The Asian man reaches out to place his hand on the soldier, who is armed with a rifle

The terrified tourist jumps back and is then seen running away, quickly learning his lesson.

The video, entitled 'Why you don't harass the Queen's Guard', was posted online earlier this week and has been viewed more than 15,000 times.

The MoD said it backed the soldier and that members of the public should show respect towards guardsmen.

Clad in their distinctive red tunics and bearskins hats, the soldiers of the Queen’s Guard are charged with protecting official royal residences.

'Get back'! The guard yells at the man as he touches him, immediately wiping the grin off his face

Armed: The soldier - charged with protecting royal residencies - points his rifle at the man, who has already scarpered

Back to work: Ever the professional, the guardsman places his gun back on his shoulder and continues his march

The units, manned by fully-trained, serving soldiers, have more than 350 years of history and have defended monarchs since Charles II took the throne after the English Restoration in 1660.

There are thought to be guidelines in place for guardsmen to deal with nuisances, which begins with stamping their feet and shouting.

Raising a rifle is considered a 'final warning', after which the guardsmen is allowed to detain the person in question.

Earlier this month, another tourist was left embarrassed after a confrontation with the Queen's Guard.

Gerry Weatherhead, 58, a retired RAF engineer from Haverhill in Suffolk, was barged out of the path of a troop of marching guardsmen outside Buckingham Palace.

Gerry Weatherhead, 58, a retired RAF engineer from Haverhill in Suffolk, was barged out of the path of a troop of marching guardsmen outside Buckingham Palace earlier this month

Oblivious to the soldiers, Mr Weatherhead was caught on video chatting to his wife as the men approached him at speed, shoving him out of the way as they marched through.

Following the collision the video shows the unconcerned soldier continuing to march while a loud military voice bellowed at Mr Weatherhead: 'Make way!'

A woman's voice can then be heard jeering: 'Stupid man!'