Until April 2003, IMBs in prisons were known as Boards of Visitors and IMBs in immigration removal centres were known as Visiting Committees.
Boards consist of members of the public who are unpaid volunteers who are appointed by the Home Secretary to fulfill this task. The success rate of applicants is about 50%. There are on average between 15 to 20 volunteers per institution. Most members serve more than three years.
Board members hold keys and have access at any time to every part of the Prison and IRC and to all prisoners and detainees.