The courts in Singapore have traditionally maintained a green light approach to judicial review. This is exemplified by a reluctance to extend existing grounds of and / or recognise new grounds of review. So, for example, irrationality review has remained at the original high and fixed threshold set in Associated Provincial Picture Houses Ltd. v Wednesbury Corporation . And on multiple occasions the courts have refused to recognise proportionality as a ground of review, even in rights-based challenges. An exception to this was the High Court’s recognition of the doctrine of substantive legitimate expectations in Chiu Teng@Kallang Pte Ltd v Singapore Land Authority  1 SLR 1047. However, the Court of Appeal subsequently indicated that it will revisit the doctrine at an appropriate juncture.
This conservative stance has been judicially rationalised on the basis of a ‘green light’ adherence to the separation of powers in a way that is suited to the political context of Singapore. However, a recent line of cases suggest a possible recalibration of the separation of powers in a way that is more red-light (or, at least, less green light). This has been through a more robust definition of the role of the judiciary as a ‘co-equal’ branch of government within the separation of powers.
This idea of co-equality of the different branches is not new to Singapore. However, until recently, ‘co-equality’ rationalised the need for judicial deference. This is apparent from, for example, the case of Ramalingam Ravinthran v Attorney-General (2012). The applicant challenged the decision of the Attorney-General (as public prosecutor) to charge him and his co-accused with different charges in relation to the same criminal enterprise under the Misuse of Drugs Act. The applicant’s charge carried the mandatory death penalty, while his co-accused’s did not. The applicant challenged the Attorney General’s decision on the ground that it was unconstitutional as an infringement of the equality guarantee under Article 12 of the Constitution. In deciding on the standard of review to adopt when reviewing exercises of prosecutorial discretion under Article 12, the Court observed (at paras 43-44):
“the prosecutorial power is a constitutional power vested in the Attorney-General pursuant to Art 35(8) of the Constitution. It is constitutionally equal in status to the judicial power set out in Art 93… In view of the co-equal status of the two aforesaid constitutional powers, the separation of powers doctrine requires the courts not to interfere with the exercise of the prosecutorial discretion unless it has been exercised unlawfully…the acts of high officials of state should be accorded a presumption of legality or regularity, especially where such acts are carried out in the exercise of constitutional powers…” (emphasis added)
The implication of the co-equal status of the Attorney-General and the judiciary was to significantly restrict the scope of judicial review. Courts can only assess whether the Attorney-General’s decision was based on an unbiased consideration of only relevant considerations. The latter was defined broadly to include the willingness of one offender to testify against others and “other policy factors”.
This can be contrasted with more recent uses of ‘co-equality’ within the separation of powers. This is reflected, most prominently, in the case of Tan Seet Eng v Attorney-General (2015). The applicant challenged a decision to detain him without trial under the Criminal Law (Temporary Provisions) Act (2000). The detainee was suspected of being involved in a global football match-fixing scandal and was detained under the legislation on the basis that he posed a threat to “public safety, peace and good order”. Earlier when the courts had purported to review preventative detention decisions (that time under the Internal Security Act), Parliament responded by amending the legislation and the Constitution to significantly restrict judicial review to the narrowest of technical grounds. These amendments were challenged in subsequent judicial review proceedings  but the courts deferred, rejecting the applicant’s arguments made against such ‘ouster’-type clauses in reliance on Anisminic Ltd v Foreign Compensation Commission (1969).
However, in Tan Seet Eng, the Court of Appeal held (at para 1 and 90):
“The rule of law is the bedrock on which our society was founded and on which it has thrived…one of its core ideas is the notion that the power of the State…is subject to legal limits….it would be meaningless to speak of power being limited were there no recourse to determine whether, how, and in what circumstances those limits had been exceeded. Under our system of government, which is based on the Westminster model, that task falls upon the Judiciary. Judges are entrusted with the task of ensuring that any exercise of state power is done within legal limits.…the Judiciary is one of three co-equal branches of government. But though the branches of government are co-equal this is so only in the sense that none is superior to any other while all are subject to the Constitution…” (emphasis added)
On the basis of this analysis of co-equality, the Court of Appeal concluded that such preventative decisions were reviewable on normal administrative law grounds (illegality, irrationality and procedural fairness). On the facts of the case the detention orders were struck down on narrower technical grounds (on the face of the detention order there was insufficient information on the grounds for detention). However, the obiter discussion on co-equality of the judiciary and the resulting scope of review is crucial. This is especially since earlier on (as discussed above) similar review of preventative detention orders under the Internal Security Act had been followed by legislative and constitutional amendments to restrict judicial review. In addition, the applicants there were re-arrested shortly after. Following Tan Seet Eng, however, the Ministry of Home Affairs issued a statement which stated that the “[Ministry] respects and accepts the Court of Appeal’s judgment”. The Court of Appeal’s decision was handed down on 27 November 2015. The applicant was shortly re-arrested on 1 December 2015 under a new detention order on 5 December 2015 that the Ministry stated was compliant with the Court of Appeal’s decision.
Tan Seet Eng and the events that followed exemplify a different interaction between the judiciary and the political branches. The political reactions, in particular, following Tan Seet Eng could be seen as a tacit acceptance of the new conceptualisation of co-equality within the separation of powers. The boundaries of this co-equality will be tested as the courts re-engage with the political branches in other areas that were typically subject to deference (including, for example, review of prosecutorial discretion).