The information you have requested is not currently published by the department. The department has written to the UK Statistics Authority (UKSA) with regard to this matter. Please see the link below:
In the Chief Statistician’s response to the UKSA, we committed to investigate whether there is data held by the Department which can inform understanding of the effect of the NRPF condition. Following our investigation, we have published information relating to change of conditions. The recent update to the Migration Transparency data in relation to change of conditions which was published on 26 November 2020, broke the data down in to further subsets of age, gender and nationality.
As the Home Office has set out to the UKSA, there are a number of reasons why it is not of practical application for the Home Office to produce an estimate of the total population subject to NRPF at any one time.
Home Office administrative data only captures information on whether visas are subject to NRPF conditions for in-country extensions. The information is not available for applications from overseas which form the majority of applications.
The information captured by the Home Office does not take into account individuals who have left the country or all those in the UK without lawful status. Therefore, they cannot be used to accurately measure the resident population subject to no recourse to public funds at any one time.