Non-ministerial government department explained

Non-ministerial government departments (NMGDs) are a type of department of the United Kingdom government that deal with matters for which direct political oversight has been judged unnecessary or inappropriate. They are headed by senior civil servants. Some fulfil a regulatory or inspection function, and their status is therefore intended to protect them from political interference. Some are headed by a permanent office holder, such as a Permanent Secretary or Second Permanent Secretary.^[1]

Overview

The status of an NMGD varies considerably from one to another. For example:^[2]

Senior officials in HM Revenue and Customs work closely with cabinet ministers. Its key policies are set each year in the Finance Act. However, neither ministers nor Parliament can interfere in day-to-day taxation decisions.
A number of NMGDs are highly independent bodies; for example the Charity Commission, Ofsted and economic regulators such as the Competition and Markets Authority or the Postal Services Commission. These bodies are "creatures of statute": they implement legislation which they have no power to change. Their political independence is assured by providing that they have the status of government departments, but are accountable only to Parliament and the courts. Their budgets are usually set by the Treasury, not by the department which set them up, and they are often funded by licence fees paid by the industries which they regulate.
The Food Standards Agency is an NMGD which was created by merging two large parts of the Departments of Health and what was then the Ministry of Agriculture, Fisheries and Food. The aim was to reassure the public (after the BSE/vCJD crisis) that decisions about food safety would in future be taken by an independent body free of political control. Because the FSA was designed to take politics out of food safety, it does not seek ministerial approval for its actions.

A list of NMGDs is maintained by the Cabinet Office, which states that the following 20 are in existence:^[3]