Somerset v Stewart
Somerset v Stewart (1772) 98 ER 499 (also known as "Somersett's case", and "v. XX Sommersett v Steuart)" is a judgment of the English Court of King's Bench in 1772 relating to the right of an enslaved person on English soil not to be forcibly removed from the country and sent to Jamaica for sale. Lord Mansfield decided that:The state of slavery is of such a nature that it is incapable of being introduced on any reasons, moral or political, but only by positive law [statute] , which preserves its force long after the reasons, occasions, and time itself from whence it was created, is erased from memory. It is so odious, that nothing can be suffered to support it, but positive law. Whatever inconveniences, therefore, may follow from the decision, I cannot say this case is allowed or approved by the law of England; and therefore the black must be discharged. 
Somerset v Stewart
Although Britain participated extensively in the Atlantic slave trade and in establishing and governing slave colonies, slave holding within England itself had not been authorized by statutory law (an act of the legislature (Parliament)), and Lord Mansfield found it also to be unsupported in England by the common law (he made no comment on the position in the overseas territories of the British Empire, which often had royal statutes). Lord Mansfield's judgment was deliberately expressed in narrow terms, and scholars and later judges have disagreed over precisely what legal precedent the case set. Lord Mansfield found it a narrow prohibition against an enslaved person being removed from England against his will. Britain continued slavery in its overseas empire for decades after the decision.
Fiat justitia ruat caelum
Fīat jūstitia ruat cælum is a Latin legal phrase, meaning "Let justice be done though the heavens fall." The maxim signifies the belief that justice must be realized regardless of consequences. According to the 19th-century abolitionist politician Charles Sumner, it does not come from any classical source. It has also been ascribed to Lucius Calpurnius Piso Caesoninus, see . It was used in "Somerset v Stewart".
Fiat justitia ruat caelum
The falling sky clause occurs in a passage of "Heauton Timorumenos", by Terence, suggesting that it was a common saying in his time. In the scene, Syrus suggests a scheme through which Clinia might deceive another into taking actions that would further his love interests. Syrus lays out his plan, while Clinia, who must act it out, finds faults with it, finally asking, "Is that sufficient? If his father should come to know of it, pray, what then?" To which the Syrus replies, ""Quid si redeo ad illos qui aiunt, 'Quid si nunc cœlum ruat?"—"What if I have recourse to those who say, 'What now if the sky were to fall?, the suggestion being that Clinia has no other options available, so to worry that the plan will, obviously, fail if the father finds out makes no more sense than worrying about the fact that it will also fail if the world were to suddenly end.

Question: What court case used the latin phrase Fiat justitia ruat caelum to declare chattel slavery was unsupported by common law in England and Wales?
Answer: Somerset v Stewart