In the UK, which ATS unit would be responsible for CTR entry clearances?
The answer depends on which aerodrome you are talking about, and can be found in the UK AIP: http://www.nats-uk.ead-it.com/public/index.php%3Foption=com_content&amp;task=blogcategory&amp;id=165&amp;Itemid=3.html

Click eAIP to open the electronic AIP. In the left menu, open the AD 2 Aerodromes section and navigate to the aerodrome in question. Then open the AD 2.17 section of that aerodrome.

In AD 2.17, airspaces related to the specific aerodrome are listed. Column 1 contains the airspace designator and lateral limits. Column 4 contains the responsible ATS unit.

As an example - the Birmingham (EGBB) CTR is controlled by Birmingham Approach.