Custody sergeant

[ashbfc 5]

Watching the force: Essex, it seems the officer behind the custody desk is dressed in blue and is a member of police staff instead of the usual custody sergeant.

Do Essex have custody sergeants? 

[Indiana Jones 391]

Probably a DDO assisting a custody sergeant. They must have a sergeant  (although a constable can act up).

[Elton the snowman 0]

Detention officers wear blue t-shirts, the custody Sargent will over see everything they do, and will authorize the detention.