In early times the Guard was as much as 100 strong and provided Escorts to accompany the Sovereign if he or she travelled by road. It now consists of either a Long Guard or a Short Guard.
When The Queen is in London, the Guard consists of 1 Officer, 1 Corporal Major (who carries the Standard), 2 Non-Commissioned Officers, 1 Trumpeter and 10 Troopers. This is known as a Long Guard.
When Her Majesty is not resident in London, the Guard is reduced to 2 Non-Commissioned Officers and 10 Troopers.
Horse Guards is named after the troops who have mounted the Queen's Life Guard on this spot since the Restoration of King Charles II in 1660 and remains the official entrance to St James's and Buckingham Palace. This is why The Queen's Life Guard is still mounted here. Apart from members of the Royal Family or cavalrymen on duty, everyone needs the Sovereign's permission in the form of an Ivory Pass to either drive or ride through Horse Guards.
The Guard Changing Ceremony takes place each weekday at 11 o'clock and at 10 o'clock on Sundays. The mounted sentries (who change every hour) are on duty each day from 10am until 4pm, at which time there is a dismounted parade of the Guard. There are two dismounted sentries on duty until the gates are shut at 8pm, when only one sentry is left on guard until 7am when the second sentry returns on duty. No one, unless in possession of the password, can gain admission to Horse Guards after the gates have been closed.