The Apprenticeship rules includes a section on this that applies to deliver training to employers who do not pay the levy and the following applies:
P276.6 Return complete data in line with the 2018 to 2019 ILR specification with key focus to critical fields. Critical fields are:
learner contact details for surveys, especially phone numbers
The household situation field is required for non-levy funded apprenticeships that start on or after 1 August 2018 and is collected at the point of enrolment (Funding model 36, ACT 2).
This requirement has been included in the ILR Specifications and guidance but is currently not covered by the validation rules, so you will not see any validation issues where you have not returned the data.
I think the ESFA and others have missed this requirement.