In A Local Authority v X and Others  EWHC 874 (Fam) Mrs Justice Gwynneth Knowles was required to consider the nature, purpose and duration of the "reasonable period”, in Article 39(2) of the Vienna Convention on Diplomatic Relations (VCDR), during which a person who has enjoyed privileges and immunities will continue to do so, after he or she has ceased to perform diplomatic functions. The court also considered whether the children of a person holding privileges and immunities retain them while in foster care.
These issues arose in the course of care order proceedings under the Children Act 1989. The children of a member of the administrative and technical staff of a diplomatic mission were taken into temporary care, after allegations of mistreatment. The local authority eventually sought a final care order to provide for long term fostering. While those proceedings were on foot, the mother’s diplomatic posting came to an end and the FCO certified (under section 4 of the Diplomatic Privileges Act 1964, the legislation which gives effect to VCDR in the UK) that her privileges and immunities ended 31 days later. Before making any order for the welfare of the children, the court had to resolve a number of jurisdictional questions: whether the FCO’s certificate was conclusive; what the duration of the reasonable period was; whether the children had remained members of the Mother’s household for VCDR purposes; and whether the court’s power to make care orders was affected by the existence of diplomatic privileges and immunities as a matter of principle.
In a carefully reasoned judgment, the judge surveyed academic commentary and the leading authorities including Estrada v al-Juffali (Secretary of State for Foreign and Commonwealth Affairs intervening)  EWC Civ 176; Al-Malki and another v Reyes (Secretary of State for Foreign and Commonwealth Affairs and another intervening)  UKSC 61 and Re B (Care Proceedings: Diplomatic Immunity)  EWHC 1751 (Fam), none of which was on all fours with the facts before her. The judge held, inter alia, that:
(a) The FCO’s certificate was determinative of facts, but the termination of privileges and immunities was a mixed matter of fact and law. The 1964 Act did not prescribe a time limit for the termination of diplomatic rights and privileges as is the case in some other countries. Under those circumstances, "the reasonableness of the period pursuant to Article 39(2) in this particular case was ultimately a matter for the court to scrutinise and determine".
(b) She accepted the Secretary of State’s submission that the reasonable period pursuant to Article 39(2) must be “strictly and exclusively” related to the purposes of VCDR privileges and immunities. What was reasonable had to be determined "in the context of inter-state diplomatic relations and on the basis of matters that the Executive is best placed to consider." Although the Secretary of State’s view, expressed in the certificate was not conclusive, it was “thoroughly and critically relevant”.
(c) The children had remained part of the mother’s “household” in VCDR terms for the duration of the time that they were in temporary foster care and so had retained the diplomatic privileges and immunities that they derived from her, for as long as those privileges and immunities lasted.
(d) Although there were no surviving diplomatic privileges or immunities that might obstruct a final care order, the Judge considered, obiter, that she would have had jurisdiction to make such an order even if there were. Article 37(2) VCDR permitted proceedings to be brought in respect of non-official acts and it would be surprising if VCDR did not also permit consequent orders to be enforced. It was well-recognised in international law that it would be contrary to the rule of law for a court to determine a person’s legal rights and then not enforce them. In any event, it was possible to envisage circumstances where the immunities accorded by the1964 Act had to be read down to be consistent with Article 3 of the European Convention on Human Rights.
This is an important judgment considering the scope of VCDR privileges and immunities under English law and it is notable for its narrow definition of the purposes of VCDR privileges and immunities and for the weight that it accords to the Secretary of State’s assessment of reasonableness. Though such matters remain ultimately justiciable, arguably the practical effect of this approach, “leaves the exercise of the prerogative untrammelled by a rival judicial inquiry” in the words of Blake J in al Attiya v Bin-Jassim Bin-Jaber Al Thani  EWHC 212 (QB). Although the issues arose in the context of the Mother's routine posting, the same analysis would apply (perhaps a fortiori) if a diplomat were to be expelled as persona non grata. The judgment also gives further support to the reasoning of Dame Elizabeth Butler-Sloss in Re B as to the court’s ability to make and execute judgments against a person holding privileges and immunities.