3.2.2.1 - Comparing UK and US Constitutions
This lesson compares the UK and US constitutions as constitutional arrangements. It covers codification, sources, sovereignty, separation of powers, checks and balances, devolution/federalism, rights protection, and constitutional amendment or change. It uses structural, rational and cultural approaches where they help explain similarities, differences and impact. Detailed teaching on UK devolution, US federalism, legislatures, executives and judiciaries is signposted only where needed for this comparison.
Comparative Lens
AQA Paper 2 does not ask for two separate one-country descriptions. It asks for comparison: how UK and US constitutional arrangements are similar, how they differ, and what those differences do to government and politics.
Constitution
The set of rules, principles and practices that establishes where political power is located, how it is exercised, how it is limited, and how constitutional rules can change.
The central contrast is this:
| Question | UK constitution | US constitution |
|---|---|---|
| Is it codified? | Partly written but uncodified. It is spread across statutes, common law, conventions, prerogative powers and authoritative guidance. | Codified in a single constitutional text with amendments. It has higher legal status than ordinary law. |
| Where is legal sovereignty? | Parliament is legally sovereign. It can make or unmake law, and courts generally cannot strike down Acts of Parliament. | The Constitution is supreme law. Ordinary federal and state law must be compatible with it. |
| How separated are the branches? | Executive and legislature are fused in a parliamentary system. The Prime Minister and most ministers sit in Parliament. Courts are institutionally separate but cannot invalidate primary legislation. | Legislative, executive and judicial powers are vested in separate branches. Congress, the President and the Supreme Court are designed to check each other. |
| How is territorial power organised? | Devolution transfers power from Westminster to Scotland, Wales, Northern Ireland and some English areas by statute. It is asymmetric and theoretically reversible. | Federalism divides sovereignty between national and state governments. State authority is constitutionally recognised. |
| How are rights protected? | Through statutes such as the Human Rights Act 1998, common law, conventions, political accountability and courts. Rights are not entrenched against Parliament. | Through the Constitution, Bill of Rights, later amendments and Supreme Court interpretation. Rights can invalidate ordinary law. |
| How does change happen? | Usually through ordinary Acts of Parliament, conventions, political practice and court judgments. | Formally through Article V amendment; informally through interpretation, precedent, federal-state practice and political custom. |
AQA gives three theoretical approaches for comparison. They are not decorative labels. They help explain why constitutional similarities and differences matter.
| Comparative approach | What it asks | Example for this lesson |
|---|---|---|
| Structural | What do the constitutional rules and institutions look like? | The UK has executive-legislative fusion and parliamentary sovereignty; the US has separated branches, judicial review and federalism. |
| Rational | What incentives do political actors face inside those structures? | A UK government with a Commons majority has incentives to use statute to deliver its programme quickly; a US President has incentives to negotiate with Congress, litigate, use executive action or appeal to states and public opinion. |
| Cultural | What political traditions and expectations shape how the rules work? | UK politics often values pragmatic constitutional evolution and conventions; US politics often treats the written Constitution, rights claims and state identity as central political language. |
The most common weak comparison is to say "the UK is flexible, the USA is rigid" and stop there. A stronger answer explains the impact. UK flexibility can make constitutional reform easier but may concentrate power in the executive if the government controls the Commons. US rigidity can protect against sudden majoritarian change but may shift conflict into courts, states and inter-branch bargaining.
Codification And Sovereignty
Codification is the most visible constitutional difference.
Codified constitution
The central constitutional rules gathered in one authoritative document, normally with higher legal status than ordinary law and a special amendment process.
Uncodified constitution
A constitution not contained in one higher-law document; its rules are dispersed across several legal and political sources.
The UK constitution is better described as partly written and wholly uncodified. It is not "unwritten" in a simple sense. Much of it is written down, but not in a single entrenched constitutional text.
| UK source | Example | Constitutional role | Limit |
|---|---|---|---|
| Statute | Human Rights Act 1998, Scotland Act 1998, Constitutional Reform Act 2005 | Creates rights duties, devolved institutions, court structures and public powers. | A later Parliament can usually amend or repeal it. |
| Common law | Judicial review principles; limits on public authority powers | Courts develop legal principles about legality, procedural fairness and executive power. | Clear statute normally prevails over common law. |
| Conventions | Prime Minister should command Commons confidence; ministers account to Parliament | Make the political system work where legal rules are incomplete. | Politically binding, but not usually directly enforceable by courts. |
| Royal prerogative | Treaty-making, some appointments, foreign affairs powers | Gives ministers legal powers historically belonging to the Crown. | Cannot usually override statute or change domestic law without Parliament. |
| Authoritative guidance | Cabinet Manual | Sets out laws, rules and conventions affecting government. | Guidance is not itself supreme law. |
The US constitution is codified. The 1787 text and its amendments set out the framework of federal government, the division of powers, the rights provisions and the amendment process. This does not mean every constitutional rule is obvious. The US Constitution still needs interpretation. However, the text has higher legal status than ordinary law.
| US source | Example | Constitutional role | Limit |
|---|---|---|---|
| Constitutional text | Articles I, II and III; Article V; Article VI | Establishes branches, amendment, supremacy and federal structure. | Text is short and often broad, so interpretation matters. |
| Amendments | Bill of Rights; Fourteenth Amendment; Twenty-Seventh Amendment | Protect rights and alter constitutional rules. | Very difficult to secure ratification. |
| Supreme Court interpretation | Marbury v Madison; later rights and federalism cases | Defines what the Constitution means in disputes. | Court membership, doctrine and political context affect interpretation. |
| Federal and state practice | Elections, state law, party rules, congressional procedure | Gives practical effect to constitutional arrangements. | Practice must operate within constitutional limits. |
Sovereignty is the deeper contrast behind codification.
| Sovereignty question | UK answer | US answer | Impact |
|---|---|---|---|
| What is legally supreme? | Parliament. | The Constitution, plus federal laws and treaties made under it. | UK courts apply Acts of Parliament; US courts may invalidate ordinary law that conflicts with the Constitution. |
| Can ordinary law change constitutional rules? | Usually yes, if Parliament passes an Act. | No, ordinary law must fit the Constitution. | UK change is easier; US change is more constrained. |
| Can one legislature bind the future? | No Parliament can usually bind its successors. | Article V amendments bind future ordinary lawmakers unless amended again. | UK entrenchment is weak; US entrenchment is strong. |
| What is the role of courts? | Courts interpret and apply law, review executive action and may issue declarations under the HRA, but do not strike down primary Acts. | Courts can declare legislation or executive action unconstitutional. | US constitutional conflict is more judicialised. |
Miller I is useful UK evidence. The Supreme Court held that ministers could not use prerogative power to trigger Article 50 if that would change domestic law and remove rights created by statute without parliamentary authorisation. This did not make the UK Supreme Court supreme over Parliament. It showed the opposite: ministers needed Parliament because statute is constitutionally superior to prerogative.
In the US, Marbury v Madison is the classic judicial review evidence. It established the principle that a law conflicting with the Constitution can be treated as void by the courts. That makes the US Constitution a legal standard against which ordinary law can be judged.
The structural comparison is clear: the UK constitution is flexible because Parliament is the highest legal source; the US constitution is entrenched because the Constitution is higher law. The rational comparison follows: UK governments focus on winning and maintaining Commons control, while US actors often pursue constitutional objectives through litigation, state-level policy, supermajority bargaining or appointments to the Supreme Court. The cultural comparison is that UK constitutional argument often sounds practical and evolutionary, while US constitutional argument often invokes founding text, original meaning, rights and constitutional identity.
Active reading: Why does parliamentary sovereignty make the UK constitution easier to change than the US Constitution?
Separation And Checks
Separation of powers
Dividing legislative, executive and judicial functions so that power is not concentrated in one body.
Checks and balances
The powers each branch has to limit, delay, scrutinise or influence the others.
The UK and US both have legislatures, executives and judiciaries. The constitutional relationship between them is very different.
| Branch/function | UK constitutional arrangement | US constitutional arrangement |
|---|---|---|
| Legislature | Parliament makes law. The House of Commons is politically dominant, especially when a government has a majority. | Congress makes federal law. The House of Representatives and Senate must both pass bills. |
| Executive | Government is drawn largely from Parliament. The Prime Minister and ministers normally sit in the Commons or Lords. | The President is separately elected and cannot sit in Congress. Cabinet members are not members of Congress. |
| Judiciary | Courts are institutionally independent, especially after the Constitutional Reform Act 2005 and creation of the UK Supreme Court in 2009. They cannot strike down Acts of Parliament. | The Supreme Court and federal courts interpret the Constitution and can strike down federal or state action that is unconstitutional. |
The UK is often described as having a fusion of powers between executive and legislature. This does not mean there are no checks. It means the main checks are political, parliamentary and legal in a different way from the US.
| UK check | How it works | Why it is limited |
|---|---|---|
| Parliamentary scrutiny | Questions, debates, committees, opposition days and votes can expose and challenge ministers. | A disciplined government majority can usually win Commons votes. |
| Ministerial responsibility | Ministers are expected to explain and defend their actions to Parliament. | Consequences often depend on political pressure, media attention and party discipline. |
| House of Lords revision | The Lords scrutinises and revises legislation. | The Parliament Acts and Commons primacy limit the Lords' ability to block most legislation. |
| Judicial review of executive action | Courts can rule that ministers and public bodies acted unlawfully or beyond their powers. | Courts generally cannot invalidate primary legislation itself. |
| Conventions | Political rules guide conduct, such as confidence and accountability. | Conventions may be contested and are not normally directly enforceable as law. |
Miller/Cherry in 2019 is a useful example of a UK legal check on executive power. The Supreme Court held that prorogation was unlawful because it frustrated Parliament's ability to carry out its constitutional functions without reasonable justification. The point for comparison is not that the UK suddenly became US-style. The point is that UK courts can police legal limits on executive power while Parliament remains legally sovereign.
The US has a clearer structural separation. The Constitution vests legislative power in Congress, executive power in the President and judicial power in the Supreme Court and lower federal courts. But separation is combined with checks and balances rather than total isolation.
| US check | Example | Impact |
|---|---|---|
| Presidential veto | The President may veto legislation passed by Congress. | Congress may need compromise or a two-thirds override. |
| Congressional override | Two-thirds of both houses can override a veto. | Prevents the President having an absolute legislative veto. |
| Senate advice and consent | Senate confirms major appointments and approves treaties by supermajority for treaties. | Gives Congress leverage over executive and judicial personnel. |
| Impeachment | House impeaches; Senate tries impeachments. | Creates a constitutional route to remove federal officers, though it is politically difficult. |
| Judicial review | Courts can rule legislation or executive action unconstitutional. | Gives the judiciary a major role in constitutional politics. |
| Power of the purse | Congress controls appropriations. | Can constrain executive priorities. |
The impact on government and politics is different.
| Issue | UK effect | US effect |
|---|---|---|
| Policy speed | A majority government can legislate quickly. | Divided government, Senate rules, vetoes and litigation can slow change. |
| Accountability | Government is directly answerable to Parliament, but a majority can protect it. | Branches can blame each other, making accountability more dispersed. |
| Executive power | Prime Ministers may be powerful when backed by a Commons majority. | Presidents have important powers but often face Congress, courts, states and fixed terms. |
| Constitutional conflict | Often resolved politically through Parliament, party pressure and statute. | Often resolved through inter-branch bargaining and litigation. |
The rational approach is especially useful here. In the UK, the Prime Minister's rational strategy is to maintain party unity and Commons confidence. In the US, the President's rational strategy often includes bargaining with Congress, using executive action, shaping appointments, appealing to public opinion and defending policy in court. The structure changes the incentives.
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