Had she known, Windsor Castle's most famous resident would not have been amused.

A couple were caught having sex on a grass bank outside the Queen's residence- as hundreds of tourists looked on.

Apparently unable to control themselves, the drunken pair stripped naked and began having sex in front of the Castle's Garter Tower in full view of a busy road and shops.

Amused Japanese tourists jostled for position as they filmed the couple.

One witness said: 'One window from the guardroom opened up and when a soldier saw what was going on he told his mates — and lots of windows opened.

'The couple did not care who was looking and just kept going as if they were in their own bedroom.

'They even ignored the Please Keep Off The Grass signs.

'A few soldiers were cheering them on from above and plenty of young people did the same from the roadside. There were camera flashes going off and people videoing.' 

Others were rather less amused: An employee at the Harte and Garter Hotel, which looks onto the castle, said guests went out to observe the scene and could not believe their eyes.

The woman, who asked not to be named, said: "I think it was going on for about ten or 15 minutes, which is quite a long time, considering the location.

While the Queen was in residence at Windsor Castle at the time, her private apartments are located far from where the incident took place.

The couple's fun, and that of the spectators, came to an abrupt end when armed Royal Protection Squad officers arrested them.

The couple were kept in cells overnight and cautioned for outraging public decency.