The poker player Phil Ivey has lost his court bid to recover £7.7m ( $10.2m) of winnings from a London casino.
The 40-year-old American has been fighting to recover the sum since successfully playing a version of baccarat known as Punto Banco at Crockfords Club in Mayfair in 2012.
The hearing at the supreme court considered whether dishonesty was a necessary element of the offence of cheating.
Ivey had challenged a 2016 majority decision in the court of appeal dismissing his case against Genting Casinos UK, which owns Crockfords. Genting said a technique he used, called edge-sorting, was not a legitimate strategy, while Ivey maintained that he won fairly.
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Five justices unanimously upheld the majority decision of the court of appeal, which dismissed his case on the basis that being knowingly dishonest was not a necessary element of “cheating”.
After the game in question, Ivey was told the money would be wired to him in Las Vegas, but it never arrived, although his stake of £1m was returned.
Genting said the technique of edge-sorting used by Ivey, which involves identifying small differences in the pattern on the reverse of playing cards and exploiting that information to increase the chances of winning, was not a legitimate strategy.
Ivey did not personally touch any cards, but persuaded the croupier to rotate the most valuable cards by intimating that he was superstitious.
In the court of appeal, Lady Justice Arden said the Gambling Act 2005 provided that someone may cheat “without dishonesty or intention to deceive: depending on the circumstances it may be enough that he simply interferes with the process of the game”.
There was no doubt, she added, that the actions of Ivey and another gambler, Cheung Yin Sun, interfered with the process by which Crockfords played the game of Punto Banco with Ivey.
Stephen Parkinson, head of criminal litigation at Kingsley Napley, the law firm that represented Crockfords, said: “This is one of the most significant decisions in criminal law in a generation. The concept of dishonesty is central to a whole range of offences, including fraud.
“For 35 years, juries have been told that defendants will only be guilty if the conduct complained of was dishonest by the standards of ordinary, reasonable and honest people, and also that they must have realised that ordinary, honest people would regard their behaviour as dishonest.
“The supreme court has now said that this second limb of the test does not represent the law and that directions based upon it ought no longer to be given by the courts.”