The Westminster parliament is sovereign. As a result, the UK is almost unique in not having a codified constitution with entrenched provisions. Parliament can enact legislation on any subject matter it likes, but it cannot bind its successors. Hence the ease with which the failed attempts to achieve a two-thirds majority requirement for an early parliamentary general election under the Fixed-term Parliaments Act 2011 could be overridden by the Early Parliamentary General Election Act 2019 when a simple majority of MPs agreed to pass it in October 2019.
The two Miller cases make it clear that courts can be used to protect parliament’s powers. The second of these also clarified that parliamentary sovereignty means parliament is more constitutionally important than the government.
In Miller I, the Supreme Court was asked whether the ‘prerogative power’ – i.e. the power of the Prime Minister, in this case over foreign relations matters – included a power to notify the EU of the UK’s intention to withdraw. The court concluded that the prerogative power did not include an ability to modify domestic law – notably the European Communities Act (ECA) 1972, which took the UK into the EU at a domestic level. Nor did it include a power to frustrate legislation, or to remove domestic rights. The court’s decision thus reinforced parliament’s role in the constitution. Its first immediate result was that primary legislation was needed to empower ministers to trigger the Article 50 process. This provided parliament with the opportunity, should it have wished to do so, to set conditions on the exercise of this power.
