The Government is committed to identifying and supporting victims of modern slavery. The National Crime Agency regularly publishes NRM data, and the number of potential victims referred into the NRM for 2018 is available online here:
Annual summary statistics for previous years are also published on the NCA website.
The statistics also show the outcomes of reasonable and conclusive grounds decisions. This data does not distinguish whether individuals are migrant detainees. Since 29th April this year the Single Competent Authority (SCA) took over responsibility for decision making in the NRM from the NCA and UKVI. Publishing of statistics for future years regarding the NRM will therefore be the responsibility of the Home Office.