In a recent decision, the Supreme Court has clarified the circumstances in which a judge who has announced his or her decision is entitled to change that decision before the order is sealed: In the matter of L and B (Children)  UKSC 8. Although the issue arose in the context of care proceedings in the family court, the same principles will apply to civil proceedings.
The Supreme Court noted that it has long been the law that a court is entitled to reverse its decision at any time before the order is drawn up and perfected (i.e. sealed by the court). This is sometimes referred to as the Barrell jurisdiction, after the Court of Appeal decision in In re Barrell Enterprises  1 WLR 19 which is generally seen to have laid down a restriction that (apart from the correction of minor errors or slips) the jurisdiction should only be exercised in exceptional circumstances.
In the present case, the Supreme Court held that there is no such restriction upon the court’s jurisdiction to revisit its own decision before the order is sealed. In deciding whether to exercise the power, the court’s overriding objective must be to deal with the case justly. It will be relevant whether any party has acted upon the decision to its detriment, especially if it was expected that they might do so before the order was sealed. Every case is going to depend upon its particular circumstances and, the court said, “a carefully considered change of mind can be sufficient”. Nonetheless, we would not expect judges to take such a decision lightly.