The unit for vulnerable prisoners at HMP La Moye has had to be extended because it was full at the end of 2024.
All 59 places on Journeaux Wing were taken in November.
An extra four beds have since been allocated to the VPU.
Average daily occupancy of the unit was 89% across the year, up eight percent on 2023 and a 15% increase on 2022.
Overall, the prison population peaked at 88% capacity in 2024, with an average of 155 inmates daily,.
That is 12% more than the previous year.
The service's annual report outlines the 'ongoing trend in population increase'.
Read: New Prison Governor appointed to HMP La Moye
There was a change in leadership at HMP La Moye during 2024, with Prison Governor Susie Richardson resigning and Deputy Governor Artur Soliwoda stepping up as Acting Governor.
A permanent successor - Paul Yates, currently prison governor at HMP Nottingham - takes the post next month.
Challenges include finding stable accommodation for prisoners on their release, with almost half of placements being transient or temporary, such as shelters or guest houses.
The service says stable accommodation is a contributing factor in successful reintegration of former inmates into the community.
79% of convicted prisoners engaged in education or vocational training courses.
78 vocational qualifications were achieved, including City & Guilds Horticulture, City & Guilds Painting and Decorating, and Barbering.
Nine prisoners undertook additional distance learning or Open University courses.
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