How to get entityreference_backreference data programmatically
OK this was my ignorance of how to use Entity Metadata Wrappers.
The way to get the value of the field_parent_user_eb field is

$wrapper = entity_metadata_wrapper("user",$some_user);
$value = $wrapper-&gt;field_parent_user_eb-&gt;value();


$value contains an array of entities which (back) reference the original $some_user.

I should have read https://www.drupal.org/docs/7/api/entity-api/entity-metadata-wrappers before posting.