The Home Office staff rely on their guidance to make decisions.
The guidance draws upon the (unlawful) definitions in Appendix EU.
Appendix EU is based on The Withdrawal Agreement.
The Withdrawal Agreement borrows heavily from Directive 2004/38.
To understand why the Home Office are wrong to refuse applications from Zambrano carers with leave to remain, requires one to read the Withdrawal Agreement and Directive 2004/38.
The Withdrawal Agreement
TITLE II
RIGHTS AND OBLIGATIONS
CHAPTER 1
RIGHTS RELATED TO RESIDENCE, RESIDENCE DOCUMENTS
ARTICLE 15 Right of permanent residence
1. Union citizens and United Kingdom nationals,
and their respective family members, who have resided legally in the host State in accordance with Union law for a continuous period of 5 years or for the period specified in
Article 17 of Directive 2004/38/EC, shall have the right to reside permanently in the host State under the conditions set out in
Articles 16, 17 and 18 of Directive 2004/38/EC.
Periods of legal residence or work in accordance with Union law before and after the end of the transition period shall be included in the calculation of the qualifying period necessary for acquisition of the right of permanent residence.
2. Continuity of residence for the purposes of acquisition of the right of permanent residence shall be determined in accordance with
Article 16(3) and Article 21 of Directive 2004/38/EC.
3. Once acquired, the right of permanent residence shall be lost only through absence from the host State for a period exceeding 5 consecutive years.
https://assets.publishing.service.gov.u ... munity.pdf
Directive 2004/38
Article 16
General rule for Union citizens and their family members
Union citizens who have resided legally for a continuous period of five years in the host Member State shall have the right of permanent residence there. This right shall not be subject to the conditions provided for in Chapter III.
2. Paragraph 1 shall apply also to family members who are not nationals of a Member State and have legally resided with the Union citizen in the host Member State for a continuous period of five years.
3. Continuity of residence shall not be affected by temporary absences not exceeding a total of six months a year, or by absences of a longer duration for compulsory military service, or by one absence of a maximum of 12 consecutive months for important reasons such as pregnancy and childbirth, serious illness, study or vocational training, or a posting in another Member State or a third country.
4. Once acquired, the right of permanent residence shall be lost only through absence from the host Member State for a period exceeding two consecutive years.
Article 17
Exemptions for persons no longer working in the host Member State and their family members
Article 18
Acquisition of the right of permanent residence by certain family members who are not nationals of a Member State
Without prejudice to Article 17, the family members of a Union citizen to whom Articles 12(2) and 13(2) apply, who satisfy the conditions laid down therein, shall acquire the right of permanent residence after residing legally for a period of five consecutive years in the host Member State.
https://www.legislation.gov.uk/eudr/2004/38/contents