IMO almost everything to do with safeguarding is to do with covering backs, not actually protecting children, but this is the official line:
"Wherever possible references should be obtained prior to the interview so that any issues of concern raised by the reference can be explored further with the referee and taken up with the candidate during interview.
References should contain objective, verifiable information and in order to achieve this, a reference pro-forma with questions relating to the candidate’s suitability to work with children and young people should be provided.
References should include:
-length of time the person has known the applicant and in what capacity;
post held with dates , salary and reasons for leaving;
-ability and suitability to work with children and young people;
skills, strengths and weaknesses and how these have been demonstrated;
any current disciplinary investigation and/or sanction;
-any allegations and/or disciplinary investigations relating to the safety or welfare of children and young people and the outcome of these (including where any sanction has expired);
-details of any criminal convictions, cautions or bind-overs;
sickness record;
-if the referee would re-employ the applicant and, if not details of why; and
verification of the identity of the referee.
The referee should be asked to confirm whether the applicant has been the subject of any disciplinary sanctions and whether the applicant has had any allegations made against him/her or concerns raised which relate to either the safety or welfare of children and young people or about the applicant’s behaviour towards children or young people. Details about the outcome of any concerns or allegations should be sought."
Almost no-one actually provides all this information in a reference response and many LA's/schools interpret "wherever possible" to mean "always"