Briefing Parliament on its annual report on Thursday, the Judicial Inspectorate of Prisons (JICS) noted that the year in review also recorded the highest number of remand detainees ever in the past decade.
The judge emphasized that their "greatest concern" revolved around defendants convicted of rape being allowed to remain on bail rather than being swiftly jailed.
Criminals could get more than a third off their prison sentences by pleading guilty under plans being considered by ministers to tackle the court backlog and prison crisis.