Slip Rule cannot be used to reverse the effect of an immigration decision
In Katsonga ("Slip Rule"; FtT's general powers)  UKUT 228 (IAC) the Upper Tribunal reviewed the ambit of rule 31 of the First-tier Tribunal Procedure Rules 2014 (often referred to as the ‘Slip Rule’) and found that the rule cannot be used to reverse the effect of a decision at the instance of a losing party.
Rule 31 reads as follows:
"Clerical mistakes and accidental slips or omissions
31. The Tribunal may at any time correct any clerical mistake or other accidental slip or omission in a decision, direction or any document produced by it, by –
(a) providing notification of the amended decision or direction, or a copy of the amended document, to all parties; and
(b) making any necessary amendment to any information published in relation to the decision, direction or document."
Mr Ockelton, Vice President of the Upper Tribunal, held:
“9. There appears to be no clear authority on the meaning and use of the "Slip Rule". It is, however, instructive to consider the authorities on the meaning of CPR 40.12, allowing the Court to correct at any time "an accidental slip or omission in a judgment or order". Despite the width of the wording in the CPR, there is an important restriction on the power given by that rule. The power is there to enable a misprint to be corrected, or to make the judge's meaning clear: Bristol-Myers Squibb v Baker Norton Pharmaceuticals Inc  EWCA Civ 414. The power cannot be used to change the substance of a judgment or order: further authorities are cited at CPR 40.12.1 in the White Book. It is because the judge can use the slip rule only to make his original meaning plain rather than to change his original decision, that the Civil Procedure Rules and the Tribunal's Procedural Rules contain no provision for consultation with the parties. Indeed it is difficult to see that the parties ought to have any input into the judge's expression of what he originally meant.
10. We do not think that the power under the slip rule enables a decision to be reversed at the instance of the losing party. Once a decision has been given in a particular sense it may be subject to setting aside under rule 32 or the appellate process.”