Her Majesty’s Inspectorate of Prisons for England and Wales (HM Inspectorate of Prisons) is an independent inspectorate which reports on conditions for and treatment of those in prison, young offender institutions, secure training centres, immigration detention facilities, police and court custody suites, customs custody facilities and military detention.
According to HMIP website:
Every Immigration Removal Centre (IRC) will receive a full unannounced inspection at least once every four years, conducted on a risk-assessed basis. The inspection lasts for one week (preceded by two days of research). If the centre holds children they are inspected every two years.
All reports can be found on HMIP website.
There is a drop down list on the left hand side of the page with many specific categories: Immigration Removal Centre Inspections, Short- Term Holding Facility Inspections or Detainee escort Inspections.
The website also allows to search using the name of the centre or serach according to year the report was published.
The most recent report on unannounced visit to Campsfield Immigration Removal Centre has been published in February 2015 and can be read here