Her Majesty's Young Offender Institution

Her Majesty's Young Offender Institution (or HMYOI) is a type of British prison intended for offenders aged between 18 and 20, although some prisons (particularly Ashfield and Huntercombe) cater for younger offenders from ages 15 to 17, who are classed as juvenile offenders. Typically those aged under 15 will be held in a Secure Children's Home and those over 15 will be held in either a Young Offender Institution or Secure Training Centre. Generally a young offender is regarded as such until the date of their 21st or 22nd birthday, whereupon he or she will be sent to an adult prison or can remain in the YOI until they turn 22 if deemed appropriate.