Wendy Sinclair Gieben has written to ministers calling for new laws to end imprisonment of 16 and 17-year-olds by the end of March.

She said that the young offender institution at Polmont was effectively an adult prison.

Prisoners under 21 are typically sent to the young offenders’ institution until they are old enough to be sent to an adult prison. But while Ms Gieben said Polmont was doing a good job, she noted that it had the same restrictions as a prison.

Figures indicate that, last year, 120 under-18s were sent to jail in Scotland.

Ms Sinclair Gieben said that sending children to young offenders’ prison – especially on remand – breached their human rights.

“We have to change the perception that people under 18 have to go to prison because their crimes are so offensive,” she said.

“In reality, the secure care system manages people with violent challenging behaviour extremely well and we need to allow them to do it.”

She acknowledged, however, that some under-18s had committed the most serious crimes.