From 3/11/08, the Mental Health Act 2007 replaces the Approved Social Worker (ASW) with the Approved Mental Health Professional (AMHP). See Approved Mental Health Professional replaces Approved Social Worker 3/11/08 for details.

From the Act before it was amended:

• an "'approved social worker' means an officer of a local social services authority appointed to act as an approved social worker for the purposes of this Act." (s145);

• and must be "approved by the authority as having appropriate competence in dealing with persons who are suffering from mental disorder." (s114(2)).

It was generally ASWs (and now AMHPs) who make applications for detention under s2, s3 and s4.