Parliament: Structure and Functions

The UK Parliament is bicameral — it has two chambers — but constitutionally it has three elements: the House of Commons, the House of Lords and the monarch. A bill becomes an Act only when all three have agreed, which is why lawyers describe the sovereign law-maker as the Crown-in-Parliament.

Element	Members	How they get there	Real-world weight
House of Commons	650 MPs	Elected by first-past-the-post, one per constituency	The dominant chamber; the government must hold its confidence
House of Lords	Over 800 peers in March 2026	Appointed, inherited or held by Church office	Revises and delays; cannot ultimately block
The monarch	One	Hereditary succession	Formal only — Royal Assent has not been refused since 1708

Two structural facts shape everything else in this topic.

• The Lords has no fixed size and no government majority. Numbers rise as prime ministers appoint peers, and because no party controls the chamber, governments lose votes there that they would win in the Commons.
• The Commons alone is elected. Every argument about the relative power of the two Houses eventually returns to this asymmetry.

Parliament is the legislature. The government — Prime Minister, Cabinet and junior ministers — is the executive. In the UK the two overlap, because ministers are drawn from Parliament, and that fusion is the reason scrutiny is difficult.

Becoming an MP is a two-stage process, and only the second stage involves the public.

Stage one — party selection. Almost every successful candidate is chosen by a political party, usually by the members of a local constituency party. Parties can shape this: shortlists, central approval lists and, in Labour's case, all-women shortlists have all been used to change who gets selected.

Stage two — election. Voters in each of the 650 constituencies elect one MP by first-past-the-post: the candidate with the most votes wins, whether or not that is a majority. To stand, a candidate must be 18 or over, be a British, Irish or qualifying Commonwealth citizen, produce ten signatures from local electors and pay a £500 deposit, which is returned only if they win at least 5% of the vote. Judges, civil servants, serving police officers, members of the armed forces and prisoners serving more than a year are disqualified.

General elections are held at least every five years. Between them, a vacancy is filled by a by-election.

Worked case study — the Makerfield by-election, 18 June 2026. Andy Burnham was Mayor of Greater Manchester and not an MP. The sitting Labour MP for Makerfield, Josh Simons, stood down to create a vacancy, Burnham won the by-election on 18 June 2026, and he was elected Labour leader unopposed on 17 July with 379 MP nominations. He became Prime Minister on 20 July 2026, having sat in the Commons for barely a month.

This is not a quirk. It is the structure working as designed: by convention a Prime Minister must sit in the Commons to be accountable to the elected chamber. The last Prime Minister to govern from the Lords left office in 1902, and in 1963 Alec Douglas-Home disclaimed his peerage under the Peerage Act 1963 and fought a by-election for exactly the same reason. The Makerfield seat was the first vacancy created deliberately to bring a party leader into the Commons since Leyton in 1965.

The specification names "the different types of Peers", so learn the categories and how each is appointed.

Type of peer	Legal basis	How they arrive	Notes
Life peers	Life Peerages Act 1958	Nominated by the Prime Minister or other party leaders, or recommended by the House of Lords Appointments Commission	The overwhelming majority of the House; the title dies with the holder
Hereditary peers	House of Lords Act 1999	92 retained when the rest were removed; vacancies were filled by a by-election among hereditary peers themselves, an arrangement under active review in March 2026	A transitional compromise, and the target of further reform
Lords Spiritual	Bishoprics Act 1878 and later statutes	The Archbishops of Canterbury and York, the Bishops of London, Durham and Winchester, and 21 other diocesan bishops by seniority	26 seats; they leave the House on retiring from their see

Three points examiners reward.

• Patronage is the dominant route in. Prime ministers nominate party peers, and the volume matters: in his first 18 months in office to early 2026, Sir Keir Starmer appointed 62 Labour peers. The House of Lords Appointments Commission, created in 2000, vets nominations for propriety and independently recommends non-party crossbenchers, but it cannot veto a party nomination.
• Crossbenchers change the arithmetic. Peers who take no party whip were the third-largest group in the House in March 2026, at around 22% of the membership. Their presence is the main reason no government has a majority in the Lords.
• The Law Lords have gone. Until 2009 the highest court in the UK sat inside the House of Lords. The Constitutional Reform Act 2005 moved that function to the new UK Supreme Court, so serving Justices are no longer members of the legislature.

Removing the remaining hereditary peers was Labour policy from 2024, and by March 2026 it was being treated as a step towards modernising the chamber rather than an open question. Confirm the current composition before quoting membership figures in an exam.

The specification asks for "the main functions" of each House. For the Commons there are five, and the third is exclusive to it.

1. Legislating

The Commons debates, amends and votes on bills. In practice the government writes almost all successful legislation and uses its majority to carry it, so this function is better described as approving legislation than originating it.

2. Scrutinising the executive

MPs hold ministers to account through question time, select committees, debates and correspondence. This is the function that gives Parliament its day-to-day purpose between elections.

3. Representing the electorate

Each MP represents a defined constituency and takes up individual grievances through casework. This function belongs to the Commons alone, because no peer has voters.

4. Supplying and sustaining the government

Ministers are drawn from Parliament, mostly from the Commons, and a government stays in office only while the Commons has confidence in it. In 1979 James Callaghan's government lost a confidence vote by 311 to 310 and a general election followed — the clearest demonstration of what this function means.

5. Debate and legitimation

The Commons is the national forum in which contested decisions are argued out. Passing a measure through an elected chamber gives it authority that an executive decision alone would lack.

A confidence and supply agreement shows functions one and four interacting: after the 2017 election the Conservative minority government relied on the DUP to win confidence motions and Budget votes, without the DUP joining the government.

The Lords shares some of the Commons' functions and adds two the elected chamber does not perform — supplying expertise and delaying — and it performs all of them differently because its members are appointed rather than elected.

• Revising legislation. This is the chamber's core work. Peers go through bills line by line, catching drafting errors and unintended consequences, and send amendments back to the Commons. Defenders of the House argue this is a genuine constitutional job rather than obstruction.
• Adding expertise. Members include former civil servants, defence chiefs, doctors, scientists, judges and academics who bring knowledge that career politicians lack. Peers can also devote more time to a bill than MPs, who face constituency demands.
• Delaying. Under the Parliament Acts the Lords can hold up most bills for around a year. Delay is not a veto, but it can be enough to force a government to negotiate, or to run a bill out of parliamentary time.
• Debating and investigating. Lords select committees on subjects such as the constitution, economic affairs and science produce long-form inquiries free of the electoral cycle.
• Supplying some ministers. A small number of ministers sit in the Lords, including the Leader of the House of Lords, so that the government can answer questions in both chambers.

The Lords does not represent the electorate, and it does not decide who governs. Those two absences define both its limits and, in the eyes of its defenders, its usefulness: a chamber that cannot claim a mandate is unlikely to try to govern.

The specification wants "the extent to which these functions are fulfilled". Two developed cases let you argue both sides.

Case one — the assisted dying bill and the revising function. The Terminally Ill Adults (End of Life) Bill was a private member's bill introduced by the backbench Labour MP Kim Leadbeater, not a government bill. It passed the Commons in June 2025 and then moved slowly through the Lords, attracting large numbers of amendments. In December 2025 Leadbeater publicly criticised the pace and warned the bill could run out of time; former ministers Justin Madders and Dame Nia Griffith, with select committee chair Debbie Abrahams, wrote arguing that an unelected chamber was over-reaching. Peers replied that a long, badly drafted bill deserves careful scrutiny, and that scrutiny takes time. The crossbench peer and economist Professor Alison Wolf made that case publicly in December 2025.

What it shows: the Lords fulfilling its revising function so thoroughly that the Commons complained. Whether that is the system working or the system failing depends on whether you weight scrutiny or electoral mandate more heavily — which is precisely the judgement a 30-mark answer needs.

Case two — the Burnham premiership and the legitimating function. Andy Burnham became Prime Minister on 20 July 2026 without a general election, after Sir Keir Starmer announced his resignation on 22 June 2026 following heavy Labour losses at the May 2026 local elections. No voter was asked. The Commons supplied both the seat and the party votes that made him leader, and its continued confidence is what keeps him in office.

What it shows: Parliament, not the electorate, selects and sustains a Prime Minister. Supporters argue this is the constitution correctly applied — the UK elects a Parliament, not a Prime Minister. Critics argue a government formed this way carries a weaker mandate than one endorsed at a general election.

"Representation" carries two distinct meanings, and strong answers separate them.

Political representation asks whether seats reflect votes. Here the Commons performs poorly. In 2024 Labour won a Commons majority of 174 — around 63% of the 650 seats — on 33.7% of the UK vote, on a turnout of 59.7%, the lowest since 2001. The combined Conservative and Labour vote share was just over 57%, a record low for the two largest parties, so the gap between the party system in the country and the party arithmetic in the chamber is unusually wide.

Descriptive representation asks whether the chamber resembles the population. The Commons has become steadily more diverse in gender and ethnicity over the past three decades, though it remains unrepresentative in occupational and educational background. The Lords is unelected, older on average and shaped by patronage, so it cannot be defended on descriptive grounds at all — its defenders argue instead that it is representative of expertise.

Question	House of Commons	House of Lords
Chosen by voters?	Yes, by first-past-the-post	No
Seats proportional to votes?	No — 63% of seats on 33.7% in 2024	Not applicable
Constituency link?	Yes, one MP per seat	None
Reflects the population?	Partially, and improving	No, and not designed to
Claims a mandate?	Yes	No

A safer judgement than "Parliament is unrepresentative" is that the Commons is democratically legitimate but disproportionate, while the Lords is undemocratic but functionally useful. Say which failing matters more, and why.

1. Writing that Parliament has two parts

Parliament has three elements: Commons, Lords and monarch. Losing the Crown from the definition costs an easy AO1 mark and makes Royal Assent impossible to explain.

2. Confusing Parliament with the government

The legislature is Parliament; the executive is the government. An answer that says "Parliament passed a law reducing benefits" when it means "the government proposed and its majority carried" has blurred the distinction the whole topic rests on.

3. Listing peer types without explaining how they are appointed

The specification says "including the different types of Peers". Name life, hereditary and spiritual peers, and say who nominates each. Patronage by the Prime Minister is the point examiners are looking for.

4. Treating functions as a list rather than an evaluation

The bullet reads "the main functions ... and the extent to which these functions are fulfilled". Most of the credit sits in the second half of that sentence. For each function, give one piece of evidence that it works and one that it does not.

5. Using undated examples

Politics is marked on currency. Write "in March 2026 the Lords had over 800 members" rather than "the Lords is very large", and attach a date to every figure you quote.

6. Balancing without concluding

The 30-mark command word is Evaluate, carrying 10 marks for AO3. Set out both sides of each function, then state which reading is stronger and why. An answer that presents two views and stops leaves the AO3 marks unclaimed.