Ong Ah Chuan v Public Prosecutor is a landmark decision delivered in 1980 by the Judicial Committee of the Privy Council on appeal from Singapore which deals with the constitutionality of section 15 of the Misuse of Drugs Act 1973 (No.

There has also been academic discussion concerning whether fundamental rules of natural justice enable the courts to examine the substantive fairness or reasonableness of laws.

The Court applied a modified version of the test to situations involving the discriminatory application of neutral laws in Eng Foong Ho v. Attorney-General (2009), and expressed the view that Article 12(1) would only be infringed in such cases where there was intentional and arbitrary discrimination, or inequalities due to inadvertence or inefficiency on a very substantial scale.

[8] In Koh Chai Cheng's case, he denied knowledge of the drugs and contended that they had been planted in the boot of his car by police informers after he had arrived in Singapore.

[19] It was observed by the Privy Council that section 15 of the MDA assigned various quantity levels to certain controlled drugs, such as 2 grams (0.071 oz) for heroin.

[29] Elaborating, Lord Diplock stated that one of the fundamental rules of natural justice in the field of criminal law is that a person should not be punished for an offence unless it has been established to the satisfaction of an independent and unbiased tribunal that he committed it.

[31] Lord Diplock rejected this argument, and instead upheld the validity of a presumption of trafficking where possession of a quantity of prohibited drugs higher than the minimum specified in section 15 of the MDA has been proved.

[35][36] The court also mentioned in passing that contending the constitutionality of capital punishment was foreclosed by the recognition in Article 9(1) that a person may be deprived of life in accordance with law.

The Privy Council explained that the Article provides for all like persons to be treated alike, and prohibits laws that impose different punishments for individuals within the same class.

In addition, Lord Diplock expressed the opinion that the appropriate boundary to be drawn between varying classes of persons is a question best left to the Legislature.

[42] In the Privy Council case Haw Tua Tau v. Public Prosecutor (1981),[43] the appellants criticised amendments to the Criminal Procedure Code ("CPC")[44] that removed an accused person's right to make an unsworn statement not subject to cross-examination, and replaced it with a power exercisable by the court to draw an adverse inference if the accused person opts to remain silent after being warned about the possible consequences of doing so.

Lord Diplock, speaking for the court, questioned if the right to silence is a fundamental rule of natural justice but found it unnecessary to decide this point as he held that the new CPC provisions provided an accused person with an inducement to testify but did not compel him or her to do so.

[45] In reaching this conclusion, the judge noted that "[i]n considering whether a particular practice adopted by a court of law offends against a fundamental rule of natural justice, that practice must not be looked at in isolation but in light of the part which it plays in the complete judicial process", and that "what may properly be regarded by lawyers as rules of natural justice change with the times".

[46] In Public Prosecutor v. Mazlan bin Maidun (1992),[47] the Court of Appeal held that the right to silence is related largely to the giving of evidence, and that there is no constitutional or statutory provision in Singapore protecting it.

Procedural due process, its extreme form represented by the formal model, deals with the manner which a law, administrative justice or judicial task is carried out.

[56] Despite these academic opinions, at present the Singapore courts are still deferential to the exercise of Parliament's legislative powers and adopt a respectful attitude towards its pronouncements.

[58] In Ong Ah Chuan, the Privy Council held that the argument that capital punishment is unconstitutional is foreclosed by Article 9(1) of the Constitution itself because it clearly states that a person can be deprived of his life "in accordance with law".

[60] However, in the subsequent case Reyes v. The Queen (2002),[61] the Privy Council found Ong Ah Chuan of limited assistance as it felt that at the time it was decided the jurisprudence on international human rights was "rudimentary".

While recognising that the Constitution provides for the prerogative of mercy by vesting power to alter punishments in the Governor-General acting on the advice of an Advisory Council.

It could not have been the intention of the framers of our Constitution to diminish the rights which Singaporeans as colonial subjects were entitled to enjoy, and to lose it on becoming independent citizens of a Republic with censorial power in their hands after freedom has taken effect.Rajah proposed that,[70] in the light of the Reyes, Hughes and Fox cases, the holding in Ong Ah Chuan that the mandatory death penalty is constitutional should no longer be relied on by the Singapore courts.

[75] Several local and foreign cases have adopted the Privy Council's approach in Ong Ah Chuan to interpreting Article 12(1) of the Constitution.

In Nguyen Tuong Van v. Public Prosecutor (2005),[74] the Court of Appeal reiterated Lord Diplock's statements and applied the reasonable relation test.

While the Court said that the Public Prosecutor was required to compare like with like[37] when deciding what charge to levy on accused persons, the present case differed from the factual situation in Ong Ah Chuan.

It was argued that this provision was violated because parliamentarians who participated in illegal demonstrations were subject to a higher mandatory fine as compared to non-parliamentarians who had committed similar offences.

In evaluating the challenge, the Supreme Court of India applied Ong Ah Chuan and identified "a rational connection between the legislative classifications and the object of the law".

Tan Yock Lin has commented that the Privy Council's approach in Ong Ah Chuan was a mere tautology as it provides a "glib answer" to any allegations of inequality.

[98] As long as the court can identify a rational nexus between a classification and the object of a statute, it will uphold the legislative policy even if it is "invidiously discriminatory, unreasonable, irrational or unjust".

Article 14 strikes at arbitrariness in State action and ensures fairness and equality of treatment.Tan Tek Seng v. Suruhanjaya Perkhidmatan Pendidikan (1996)[101] applied the principle in Maneka Gandhi.

The Court of Appeal held that sections 8 and 10 were not arbitrary as "they provide for the exercise of the power to detain only for specific purposes"[105] and therefore "bore a reasonable relation to the object of the law".

[111] Approaches differing from the Ong Ah Chuan reasonable relation test have been applied to guarantees of equal protection in other jurisdictions.