Although there are estimates of the number of undocumented migrant families resident in the UK,
there are currently no estimates at local authority level. As a result, undocumented migrant families are
often invisible in local discussions of child poverty and safeguarding, can be excluded from services
to safeguard their welfare, and face the risk of destitution. This paper explores the Delphi method as a
way of using expert consensus to estimate numbers of undocumented migrant families. Fieldwork was
completed in Birmingham, West Midlands, but uses a methodology transferrable to other areas. A median
estimate of 1,500 families, containing 1,900 children was reached. The paper concludes with a discussion
of the methodological difficulties encountered, and recommendations for use of the method in the future