OK solved it
The record source of the Organisation_Details form was
SELECT organizations.*, Persons.PERSON_ID_, Persons.TITLE_, Persons.FIRST_NAME_, Persons.LAST_NAME_, Persons.POSITION_, Persons.TEL_, Persons.E_MAIL_ AS E_MAIL__Persons
FROM organizations INNER JOIN Persons ON organizations.ID_ = Persons.ORGANIZATION_FK_1_;
Change the INNER JOIN to a LEFT JOIN
SELECT organizations.*, Persons.PERSON_ID_, Persons.TITLE_, Persons.FIRST_NAME_, Persons.LAST_NAME_, Persons.POSITION_, Persons.TEL_, Persons.E_MAIL_ AS E_MAIL__Persons
FROM organizations LEFT JOIN Persons ON organizations.ID_ = Persons.ORGANIZATION_FK_1_;
and it works