6.2, 6.2.1, 6.2.2 - Comparing constitutions and federalism

Sources and constitutional authority

A constitution establishes how public power is organised, exercised and limited.

The US Constitution is codified: a central written constitutional document, supplemented by amendments, has superior legal authority. Articles I, II and III establish Congress, the presidency and the judiciary. The Bill of Rights and later amendments add protections and alter arrangements, including direct Senate elections. Statutes, judicial decisions and conventions still matter; codification does not put every operating practice in one document.

The UK constitution is uncodified, with rules drawn from several sources: Acts of Parliament, common law developed by courts, conventions, authoritative works and relevant treaties. Examples include the Human Rights Act 1998, the Scotland Act 1998 and the Constitutional Reform Act 2005. “Uncodified” does not mean unwritten: much of the constitution is written, but it is not consolidated into one superior constitutional text.

Both systems value the rule of law, meaning that public power is subject to law. Their ultimate legal authority differs. US constitutional supremacy allows a court to disapply a statute that conflicts with the Constitution. UK parliamentary sovereignty means that Westminster can make or change legislation and that courts generally cannot invalidate an Act of Parliament. The UK is a constitutional monarchy with a parliamentary government; the USA is a republic with a separately elected president. These differences affect the route by which a disputed power is challenged, rather than making one country's constitution “real” and the other's absent. US constitutional text, Parliament on sovereignty.

Changing constitutional rules

The procedure for changing a rule affects how securely it constrains a temporary governing majority.

US Article V separates constitutional amendment from ordinary legislation. The route used for all adopted amendments requires proposal by two-thirds of each congressional House, followed by ratification by three-quarters of the states, through legislatures or conventions as Congress specifies. With 50 states, ratification requires 38. An alternative proposal route involves a convention requested by two-thirds of state legislatures; it has not produced an adopted amendment. A president has no constitutional veto over an Article V amendment proposal.

In the UK, constitutional statutes ordinarily use Parliament's legislative process. There is no general Article V equivalent requiring a special parliamentary supermajority and state ratification. The creation of devolved legislatures and the UK Supreme Court through Acts demonstrates the ability to make major constitutional changes through legislation. Referendums and consultation can give changes political legitimacy without creating one universal legal amendment formula.

The comparison creates a real debate. US entrenchment can protect settled rights and prevent a small electoral majority from rewriting the system. It can also obstruct broadly desired reform and move disputes towards judicial interpretation. UK flexibility can let elected representatives respond to problems, but a government with Commons support may alter constitutional rules with less formal cross-party consent. Neither argument means change is impossible in the USA or politically easy in the UK. Courts, conventions, public opposition and electoral consequences influence change in both.

The precise US thresholds come from Article V; the consequences above are reasoned interpretations of those rules, rather than a claim that the text endorses one view of reform. Article V.

Separation, fusion and checks

Both systems check executive power, but they combine independence and cooperation differently.

US separation of powers gives legislative, executive and judicial branches distinct responsibilities and personnel. Members of Congress cannot simultaneously hold executive office. Checks and balances make the branches interact: Congress legislates and controls appropriations; the president may veto a bill; Congress can override a veto with the required supermajorities; the Senate considers important appointments; courts review legality and constitutionality. Separation means distinct offices, not that branches never affect one another.

The UK has substantial fusion between executive and legislature. Ministers usually sit in Parliament, the prime minister normally leads the Commons' governing majority and a government depends on Commons confidence. This assists coordination, but may weaken ordinary scrutiny when MPs consistently support their own party's ministers. Opposition questions, select committees, legislative defeats, the Lords' revision and independent courts provide checks. The judiciary is institutionally separate from government and Parliament, even though executive and legislature overlap.

Compare a shared dimension: can an executive avoid legislative scrutiny? US Congress possesses its own constitutional powers and electoral mandate. In the UK, the Supreme Court's September 2019 Miller/Cherry decision held the prorogation unlawful because its effect unjustifiably prevented Parliament from carrying out its constitutional functions. It checked executive action and protected Parliament; it did not strike down a Westminster Act. Formal fusion therefore does not mean unlimited prime-ministerial authority. Miller/Cherry case and judgment.

If you sit in 2027: Issue 3's glossary calls the legislature, executive and judiciary the three key “bodies”; Issue 4 calls them “branches”. The relevant distinction is between their powers and personnel, not simply whether their buildings differ.