Re Y (Experts and Alienating Behaviour: The Modern Approach) [2026] EWFC 38

Re Y is a key case concerning the modern approach to expert evidence and alienating behaviour in family law. The parents in this case separated in 2014, and proceedings concerning the children’s living arrangements commenced in 2018. Both parties made allegations of domestic abuse, including coercive and controlling behaviour. A fact-finding hearing was directed following a Cafcass recommendation that the court must make a determination in respect of these allegations.

Before any factual determination took place, the court approved the instruction of Ms Melanie Gill as a single joint expert psychologist. Ms Gill was neither registered with the Health and Care Professions Council nor a chartered psychologist. Her report, filed in September 2019, concluded that the mother exhibited significant psychological dysfunction and had alienated the children from the father. At the October 2019 hearing, the judge heard oral evidence from Ms Gill and, without hearing any other witnesses, accepted her conclusions. The children were subsequently moved to live with the father in December 2019 and all contact with the mother ceased.

This was reaffirmed in 2020, and later attempts by the mother to challenge them were unsuccessful until she issued the present Part 18 application in 2025.

Issues

The central issue in this case was whether there were grounds to revisit and set aside the earlier findings of fact. This required the court to assess whether the original process adhered to established principles governing fact-finding and expert evidence, particularly in the context of allegations of alienating behaviour (not “parental alienation”).

Decision

The President of the Family Division set aside the earlier findings and determined that there was no utility in re-litigating the underlying allegations. The court ordered that future welfare decisions be made without reliance on those findings.

The court held that the original proceedings were fundamentally flawed because they reversed the proper relationship between judicial fact-finding and expert evidence. The trial judge had relied on the expert’s opinion without first determining the factual matrix, particularly the serious allegations of domestic abuse. This amounted to a breach of the long-established principle that the court must determine the facts before expert opinion can be properly evaluated. The President emphasised that the mother’s submission at the time, i.e., that a fact-finding hearing was necessary to contextualise the allegations, had been correct. The failure to follow that course rendered the judicial determination unsafe.

A further error lay in the instruction and use of Ms Gill as an expert. She was unregulated and was not qualified within the meaning of professional standards. The court held that such an expert should not have been instructed at all. More importantly, her evidence was treated as determinative of fact, rather than as advisory, which compounded the procedural unfairness.

Further, the matter was inconsistent with the modern approach to alienating behaviour, as set out in Re C (‘Parental Alienation’; Instruction of Expert) [2023] EWHC 345 and the Family Justice Council 2024 Guidance on alienating behaviour. That approach requires the court to begin with the child’s reluctance or refusal to engage with a parent and then to determine whether that response is an appropriate reaction to abuse or other factors alongside considering whether alienating behaviour has occurred. In cases involving cross-allegations of domestic abuse and alienating behaviours, the abuse allegations must be determined first. The trial judge’s decision to bypass that stage and proceed directly to a finding of alienating behaviours was therefore fundamentally wrong. The President further stressed that alienating behaviour is not a clinical diagnosis but a question of fact for the court. Experts cannot determine whether alienating behaviours have/are occurring; they can only assist the court to establish the facts.

Finally, the judgment identified a broader systemic failure. Responsibility for the flawed process did not lie solely with the trial judge but extended to all professionals involved, including Cafcass, the children’s guardian, the local authority and legal representatives. The case illustrated how a collective failure to adhere to established principles could lead to profoundly harmful outcomes for children and families.

Conclusion

The judgment establishes that, in future, the court should not grant permission to instruct a psychologist unless they are registered with a relevant statutory body. Departure from this requirement will only be justified in exceptional circumstances and must be explained in a judgment.

It also reinforces that expert evidence must follow, not precede, judicial fact-finding. Where domestic abuse is alleged, those allegations must be determined before any assessment of alienating behaviour can properly take place. The question of whether alienating behaviour has occurred is one of fact for the court and cannot be delegated to an expert.

The judgement can be found here: https://www.judiciary.uk/wp-content/uploads/2026/02/Re-Y-judgment-final-version.pdf.