Colnbrook IRC, Heathrow

Colnbrook was built to a Category B prison standard and opened in 2004. Until September 2014 it was operated by Serco. Since then Mitie Care and Custody has held the joint Heathrow IRC contract covering Colnbrook and Harmondsworth. The site holds adult men under immigration powers ahead of removal or release^[3]GOV.UK.

HM Inspectorate of Prisons last conducted an unannounced inspection between 20 January and 6 February 2025. Inspectors found that Colnbrook continued to be well led with reasonably good outcomes for detainees, with a calm atmosphere, increased staff numbers and improved access to education. They also flagged inconsistent safeguarding and underuse of the Rule 35 process designed to protect vulnerable detainees, including cases where individuals were detained despite being assessed as unfit for detention by healthcare staff on arrival^[1]GOV.UK.

At an indicative IRC bed-day rate of £350, the 396 places at Colnbrook imply an annual run-rate of roughly £50.6 million if fully utilised. The May 2025 NAO accommodation report tracked the £1.296 billion asylum hotel bill separately from detention costs but identified detention modalities as among the most expensive options for the public purse^[4]NAO.