无限期关押（某人）
to keep someone in prison for as long as the courts feel is necessary
She was convicted of murder in 2008 and detained at Her Majesty's pleasure.
Walker was ordered to be detained at Her Majesty's pleasure after a trial at Stafford Crown Court.
The judge sentenced her to be detained at Her Majesty's pleasure for very many years.
He was originally sentenced to be detained at Her Majesty's pleasure.
The cases of 110 youngsters currently being detained at Her Majesty's pleasure are to be reviewed.
See also: detain