Question to the Ministry of Justice:

To ask the Secretary of State for Justice, what estimate he has made of the size of the prison population in (a) 2020, (b) 2025, (c) 2030 and (d) 2050.

The Ministry of Justice publishes, as National Statistics, a projection of the prison population over either (i) the period to the end of the current Spending Review or (ii) 4 years, whichever is longer. The department does not produce longer term projections.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/480031/prison-population-projections-2015-2021.pdf