Baroness Ruth Henig asked the Government about business licensing of the security sector and the licensing of private investigators in the House of Lords on 26th March 2015.  Government response was that they are committed to this and it will be introduced as soon as possible in the next Government.

See the House of Lords question and answer session here at 11:14.42:

IQ Verify can offer accreditation for BS102000, British Standard for investigative services.  Please call Lynn or Jess on 01527 910 862 for details.