Lord Pannick and the judges go to battle over a key argument in the Article 50 case
On day three of the case, Pannick, who is representing lead claimant Gina Miller, went back-and-forth with the court's 11 justices on the legal weight of June's referendum on whether Britain should leave the European Union.
At one stage, Pannick said that the judges were asking him questions that were designed to "divine a purpose, intention and effect from the act [2015 referendum act] that simply isn't there."
The queue of people seeking to enter the Supreme Court on Wednesday morning was nowhere near as large as it was on the opening day of proceedings when a long line of curious members of the public snaked around the Westminster building hours before the appeal got underway.
The crowds of protesters who gathered outside the court on Monday were nowhere to be seen, either, with just a small handful of sign-wielding Europhiles in attendance. It appears that the initial excitement surrounding the historic legal case has died down as the case becomes more complex and the arguments more technical in substance.
But Wednesday morning's session provided about as much excitement as you could hope to elicit from a case on constitutional law, with Pannick going toe-to-toe with the judges, who probed him with searching questions all morning.
The debate centred on the 2015 referendum act and the legal weight it gave to the result of the subsequent referendum on Britain's EU membership.
The judges accepted that the referendum was merely advisory, but put to Pannick that the "enormous significance" of the national vote meant it would be "surprising" if it didn't have some sort of legal impact.
Pannick argued that the 2015 referendum act was a "limited act with a very specific purpose" and added that "the referendum is a very important matter but has nothing to do with the issue before the court which is who has the power to trigger Article 50."
The exchange was probably Pannick's biggest test of the case so far.
Nevertheless, he stood his ground and delivered his case with conviction. "The court has to look at the language of the governing instrument [the 2015 referendum act]. There is nothing in it that begins to support the contention that concerns the court," he added.
"The issue of the division between the executive and the legislature has got nothing to do with the 2015 act."
He was then interrogated on why parliament had not chosen to limit the royal prerogative powers prior to the referendum taking place, a point that government lawyers Attorney General Jeremy Wright QC and James Eadie QC raised on Monday morning.
Pannick argued that it had not been necessary for parliament to push for limitations because the role of parliament and the government, in this case, is a matter of "basic" constitutional law. "It is not surprising that parliament has not directly addressed the question whether ministers can use prerogative powers," he said.
"The principle is so basic that parliament need not address the question."
He closed his argument with: "The eloquence of Eddie's appeal should not be allowed to skew the basic constitutional principles his arguments seek to violate."
The case continues and will conclude on Thursday, with a verdict expected in early January.