In any case, there is insufficient state practice to demonstrate that customary international law regards the mandatory death penalty as an inhuman punishment.

Following this case, the appellant Yong Vui Kong unsuccessfully challenged the process by which the President grants clemency to convicted persons on the advice of the Cabinet.

The motion was heard by Justice Woo Bih Li, who granted a stay of execution pending a decision by the Court of Appeal of Singapore.

The Court of Appeal noted that if the appellant's challenge on the basis of Article 9(1) was successful, it would mean that mandatory death penalty provisions in statutes other than the MDA would also be unconstitutional, such as the penalties of the following offences:[9] Yong's first argument was that the word law in Article 9(1) did not include laws that imposed inhuman punishments.

[24] The Court of Appeal indicated that many of the cases had been distinguished in its earlier decision Nguyen Tuong Van v. Public Prosecutor (2005),[25] and that this was merely "traversing old ground".

The Privy Council held that the mandatory death penalty imposed in this case contravened section 7 of the Constitution of Belize as it was inhuman or degrading punishment.

[21] The Eighth Amendment to the United States Constitution prohibits cruel and unusual punishment, and the Court proceeded on this basis to strike down mandatory death penalty legislation on a 5:4 majority.

The reasons given were that the mandatory death penalty imposed a process which did not take into account relevant differences between the offenders and the offence, and excluded from judicial consideration any mitigating factors.

[29] Similar arguments to those in Woodson were canvassed, namely, that this provision of law deprived the Court of the chance to use its discretion and wisdom and ignored all factors pertaining to the gravity of the offence.

[30] In response to the first challenge to Article 9(1), the Attorney-General Walter Woon submitted that the courts should hold to the established principles in both Ong Ah Chuan v. Public Prosecutor (1980)[31] as well as Nguyen Tuong Van.

He argued that since customary international law prohibited mandatory death penalty sentences as inhuman, the MDA provisions also violated Article 9(1).

Yong's argument was based on the fact that there are a diminishing number of states which still retain the mandatory death penalty for drug-related offences.

[34] Furthermore, the Attorney-General disagreed with the contention that the mandatory death penalty violates any customary international law prohibition against inhuman punishment.

He submitted that the decisions after Ong Ah Chuan and Nguyen Tuong Van were reflective of the Privy Council's changing attitude toward the mandatory death penalty specifically, but did not reflect any international consensus that the mandatory death penalty is prohibited by the rules of customary international law.

This was evident from the fact that there are still 31 states worldwide which continue to impose the mandatory death penalty for drug-related offences as well as other serious crimes.

This dissimilarity in circumstances would justify discriminatory punitive treatment as long as it was not purely arbitrary and bore a reasonable relation to the social object of the law.

Six points were raised to support this contention:[36] In response, the Attorney-General cited the two-step "reasonable classification" test applicable to Article 12(1) that had been outlined in Nguyen Tuong Van – that a differentiating measure in a statute is valid if:[37] The Attorney-General submitted that the 15-gram differentia was intelligible and bore a rational relation to the social purpose of the MDA: to have a deterrent effect on drug trafficking in or through Singapore by large-scale drug traffickers.

[39] It relied on the judgment of Lord Diplock in Ong Ah Chuan which stated that while it was possible for the offence of murder to be committed in the heat of the moment, it was "more theoretical than real in the case of large scale trafficking in drugs, a crime [for] which the motive is cold calculated greed".

The Court held that there is a lack of extensive and uniform state practice that supports the contention that customary international law prohibits the mandatory death penalty as an inhuman punishment.

However, the matter of what would constitute a better differentia was one which reasonable people may not necessarily agree on, and so this was a question of social policy best left to the legislature, not the judiciary.

[58] Legal observers opined that the move was unprecedented, as petitions for judicial review are usually reserved for executive actions and not processes entrenched in the Constitution.

[60] In a judgment delivered on 13 August 2010, Justice Steven Chong dismissed the application, ruling that the power to grant a pardon lies with the Cabinet and not the President.

It affirmed the High Court's view that the President did not possess any personal discretion when exercising the clemency power, and was required to act in accordance with Cabinet's advice on the matter.

[64] Nonetheless, the use of the power could be judicially reviewed if it was exercised in bad faith for an extraneous purpose, or in a way that contravened constitutional protections and rights.

[65] In addition, the Court was of the opinion that the clemency process could not be regarded as having been tainted by a reasonable suspicion of bias due to the Law Minister's remarks.

The Minister had merely been setting out the Government's policy of taking a tough approach towards serious drug trafficking offences by imposing a mandatory death penalty as a deterrent.

The alternative view was untenable, as it would mean that once any minister spoke about the Government's policy on the death penalty in a way that showed predetermination of the issue, the entire Cabinet would be disentitled from advising the President on how he should exercise the clemency power.

[67] Malaysian Foreign Minister Anifah Aman subsequently sent an appeal for clemency on Yong's behalf to the Singapore Government in July 2010.

Nathan to spare Yong's life – bearing 109,346 signatures gathered from petitioners in Sabah, other parts of Malaysia, Singapore, and online – was delivered to the Istana, the President's official residence.

[69] In January 2013, the Singapore government changed its laws to remove the mandatory death penalty for drug traffickers who merely acted as couriers, or had mental illnesses at the time of their offences.