In The Scout Association of the United Kingdom, Scout Groups can have any number of Beaver Scout Colonies, Cub Scout Packs and Scout Troops, depending on the numbers of young people and leaders available. A Scout Group can also include a Scout Active Support Unit, and an Explorer Scout Unit may be attached to a Group, although the Explorer Unit remains under the control of the district rather than the group. Scout Groups in the United Kingdom are numbered according to their formation, although not all groups follow this rule. Initially, The Scout Association reserved registration numbers for troops or Groups not attached to a church, so a Scout Group attached to a church may have been registered as 7th Gloucestershire even though it was the first formed in the location. Sometimes, Scout Groups adopt new names (for example, the 1st Whitley Scout Group became the 43rd Reading (1st Whitley) Scout Group) as District boundaries are moved and reformed. When a Scout Group is registered, a Certificate of Registration is issued by Scout Headquarters, confirming the group's registration name which may differ from its own name. Groups may also register as Sea Scout Groups or Air Scout Groups.