The Lay Observers (LO) said the treatment of young people was unacceptable and a “matter of embarrassment for the criminal justice system. LO comprises volunteers who inspect court custody conditions and transport arrangements for detainees.

The litany of custody failures included “filthy cells”, an absence of sanitary products and “complicated” transport arrangements for detainees.

In one case, a 14-year-old boy was held in a cell for 11 hours for an hour-long court hearing before magistrates in Bradford. In another a 16-year-old girl in Plymouth was sentenced in the afternoon but was kept in custody until 10pm, when she was taken on a 235-mile journey to a secure training centre near Rugby, arriving at 3am.

A Ministry of Justice spokesperson said: “The welfare of young and vulnerable people is a priority. New contracts which begin next month will place greater emphasis on improving decency and welfare for those in custody and minimise time in cells.”

John Thornhill, the national chairman of LO, said: “It is clear some people have to appear in court having travelled hundreds of miles; others are not supported with their medical conditions or disabilities; some are then kept in dirty court cells for hours on end. This is a matter of embarrassment in a modern criminal justice system.”