(a) The Home Office records the number of individuals that have received a positive Conclusive Grounds decision and this information is published quarterly by the National Crime Agency, found at http://www.nationalcrimeagency.gov.uk/publications/national-referral-mechanism-statistics.
As NRM referrals, Reasonable Grounds and Conclusive Grounds decisions are considered separately from immigration enforcement action, there is no central record of those who have received a positive Conclusive Grounds decision and are detained under immigration powers. The Home Office therefore does not collate or publish the data requested
(b) The Home Office record the number of all individuals referred to the National Referral Mechanism (NRM) and this information is published Quarterly by the National Crime Agency, found at http://www.nationalcrimeagency.gov.uk/publications/national-referral-mechanism-statistics.
This information does not distinguish between those detained under immigration powers and those living in the community. The reason for this is two-fold, firstly because the NRM referral is not an immigration route by which individuals should regularise their stay in the United Kingdom and, secondly, because a person’s status in immigration detention is not permanent and can change.
The use of immigration detention in all cases is subject to regular reviews and consequently a change in circumstance may result in a different consideration. It is quite possible that an immigration detainee is referred to the National Referral Mechanism during a detention period and is released into the community at any point during that process.