Membership and affiliation within political parties in the United Kingdom are governed by various eligibility criteria and behavioural expectations. Most parties restrict membership to individuals who meet age and citizenship requirements, share the party's core principles, and agree to abide by its constitution and rules. Members are typically prohibited from joining or supporting rival political organisations or from standing against officially endorsed candidates. In addition to full membership, some parties offer forms of associate or supporter status, which allow limited participation without the obligations of full membership. Whilst these rules help preserve party integrity and cohesion, they also define the extent to which individuals can engage with political life in the UK. Supporters without formal membership may contribute to campaigning or fundraising, but generally have fewer rights in internal decision-making or leadership elections.

History Membership of political parties has been in decline in the UK since the 1950s, falling by over 65% from 1983 (4 per cent of the electorate) to 2005 (1.3 per cent). In 2022, 1.5% of the British electorate were members of the Conservative Party, Labour Party, or the Liberal Democrats. Typically party affiliation allows an individual to support only a single party. However, two notable exceptions to this are: the Co-operative Party which permits its members to also have membership of the Labour Party and the Social Democratic and Labour Party (SDLP); and the Scottish National Party, which permits membership of Plaid Cymru.

According to the UK Parliament website sourced from a report by Olympic Britain, during the 1950s there were 2.8 million members of the Conservative Party and 1 million Labour Party members. In the years after 1945 until the early 1990s, supporters of the Socialist and Cooperative parties and trade unions linked with the Labour Party increased the overall Labour Party movement by 5 to 6 million, from which point they began to fall and currently number about 3.5 million.

Despite being founded in 1900, the Labour Party did not begin keeping track of its membership until 1928. On the other hand, the Conservative Party rarely releases their total membership statistics; additionally, there are no clear membership statistics for the Conservative Party before 1945. It is estimated that between World War I and World War II, membership levels were around 1.5 million; however, exact numbers are unknown. As of March 2026, the sum of membership numbers of UK political parties stands at ~1.25m members, or roughly 2.6% of the electorate.

Graphical summary

The charts below show how political party affiliation has varied in previous years, the parties shown currently have greater than 10,000 members reported since the start of 2025, or had over 25,000 members historically.

The chart below shows how party affiliation has varied since the 2024 United Kingdom general election, with the end of the graph on the right reflecting when the next general election can last be held.

Current membership

Party Current membership Date RegionReform UK268,00012 December 2025United KingdomLabour Party264,75431 December 2025United KingdomGreen Party of England and Wales230,000+7 May 2026Restore Britain130,00016 June 2026United KingdomConservative Party123,000July 2025 (date reported)United KingdomLiberal Democrats60,0009 United KingdomScottish National Party (SNP)56,011June 2025ScotlandYour Party55,00029 November 2025United KingdomCo-operative Party13,43031 December 2024United KingdomScottish Greens10,0005 December 2025ScotlandSinn Féin10,000September 2024Northern IrelandPlaid Cymru10,0002024WalesWorkers Party of Britain7,469January 2025Great BritainSocial Democratic Party (SDP)3,40031 December 2024United KingdomSocialist Workers Party2,5042023Great BritainEnglish Democrats2,5002015EnglandHomeland Party1,30019 May 2025United KingdomCommunist Party of Britain (CPB)1,270https://search.electoralcommission.org.uk/Api/Accounts/Documents/27252 20 August 2025 Great BritainGwlad645March 2025WalesOfficial Monster Raving Loony Party45731 December 2024United KingdomNational Liberal Party3212024Great BritainSocialist Party of Great Britain3002023Great Britain

Labour Party In the Labour Party's 2020 leadership election 490,731 people voted, of whom 401,564 (81.8%) were full members, 76,161 (15.5%) had affiliated membership and 13,006 (2.6%) were registered supporters. The registered supporter class was abolished in 2021.

In 2025, the Labour Party's membership was recorded as 264,754.

Conservative Party The Conservative Party's membership was revealed as 131,680 at the end of the 2024 Conservative Party leadership election.

Liberal Democrats The Liberal Democrats membership increased sharply after the confirmation on 18 April 2017 of the 8 June 2017 general election. Membership again increased sharply in the period before and after the two elections of May 2019, for the UK Councils and the European Parliament, though it fell again after the general election that year.

Scottish National Party There was a huge surge in membership after the 2014 Scottish independence referendum, prior to which the SNP had just over 25,000 members. Membership peaked at over 125,000 in August 2018, before falling by tens of thousands in the final years of Nicola Sturgeon's leadership.

Reform UK Membership increased by over 50% from 31,000 to 45,000+ in the eight days after Nigel Farage announced he would be returning to lead the party.

Restore Britain Restore Britain experienced rapid membership growth following its launch as a political party on 13 February 2026. On 16 February 2026, the party announced that it had reached 50,000 members just days after its formation. Two days later, party leader Rupert Lowe said that membership had risen to 70,000. The party subsequently surpassed 96,000 members by 3 June 2026. On 16 June 2026, The Times reported that Restore Britain had 130,000 paying members.

Green Party of England and Wales On 31 December 2015, the Green Party of England and Wales announced its membership as 63,219, its highest known membership up to that date. On 19 September 2025, it was revealed that the party had reached over 75,000 members. Less than a month later, on 9 October 2025, the party tweeted it had reached 95,000 members, a day after announcing it had surpassed 90,000. This "surge" has been accredited to their new leader, Zack Polanski, who was elected a month prior. On 12 October 2025, the party reached a record-breaking 100,000 members, marking an over 45% increase since Polanski was elected, and as of 13 April 2026, the Green Party has over 226,000 members.

Co-operative Party Though the Co-operative Party stands joint candidates with the Labour Party, their membership bases are independent (members have the option of joining both parties).

Enforcement There are few high-profile cases of membership criteria enforcement and as such tend to happen under exceptional circumstances.

2015 Labour leadership election

During the 2015 Labour party leadership election it emerged that 260 former candidates from the Green Party, Left Unity and the Trade Union and Socialist Coalition had attempted to become registered supporters, but were subsequently blocked from voting. Shortly before this, it was revealed that Conservative MP and former junior minister Tim Loughton had been caught applying to become a registered Labour supporter, subsequently claiming that his intention was to "blow the gaff on what a complete farce the whole thing is". Veteran Labour MP Barry Sheerman also joined calls for the election to be "paused" over the fears of infiltration by other parties. The Labour Party told representatives of the four candidates at a meeting on 11 August that 1,200 members and supporters of other parties had been excluded and a further 800 were under investigation. Harriet Harman at the time admitted that as many as 100,000 people may be blocked from voting.

The number of those rejected eventually reached 56,000, around 9.1 per cent of the 610,753 considered eligible to vote at the start of the contest. According to the party, 45,000 of those were rejected for not being on the electoral register. Labour also confirmed that it would cancel supporters' votes after they had been cast, if it was found that they were members of other parties. A number of high-profile individuals have been blocked from voting, including Marcus Chown, Jeremy Hardy, Douglas Henshall, Ken Loach, Francesca Martinez, Mark Serwotka, Pete Sinclair, Mark Steel, Luke Wright and Toby Young.

Andrew MacKinlay, a former Labour MP, further alleged that Labour was attempting to rig its own leadership election against Corbyn; a view shared by Jeremy Hardy. Such allegations became known to the media – and particularly Corbyn supporters – as the "Labour Purge", with #LabourPurge trending on Twitter. Claims of such a "purge" of Corbyn supporters were rejected by Harman who insisted that the exclusion processes were impartial to candidates. Scottish newspaper The National printed a page-long satirical cartoon speculating further vote-rigging by Labour's leadership.

Brexit

Conservative peer Michael Heseltine had the whip removed in 2019 after expressing his intention to vote Liberal Democrat. Conservative policy appears to make such expulsions discretionary, despite threats from Conservative Campaign Headquarters. Tony Blair's support for pro-remain parties led to questions about why he had not been expelled from the Labour Party. Alastair Campbell was expelled from the Labour Party after saying he voted for the Liberal Democrats in the 2019 European election. Many Labour members came out in support of Campbell using the hashtag #expelmetoo, reporting that they had similarly voted for the Liberal Democrats or other remain parties.

Criteria for membership

PartyMembership restrictionsLabour Party"are not members of political parties or organisations ... declared ... ineligible for affiliation to the party."

"[Must not stand in] opposition to a Labour candidate"

"[Must not support] a political organisation ... who stands against an official Labour candidate"Reform UK"Membership of the Party shall be open to any natural person who shares the objectives and core beliefs of the Party and who agrees to abide by this Constitution and any Rules which may from time to time be made by the Board [...]"

"Notwithstanding anything in Article IV of this Constitution, the Board may from time to time make Rules concerning the refusal of or exclusion from membership of persons or classes of persons whose admittance to membership of the Party would, in its opinion, be inimical to the interests of the Party."

"The Party Chairman (or, in his absence, his designated deputy) shall, without reservation or qualification, be entitled, to refuse to admit any person to membership.""Membership is open to any person who subscribes to the object of the Party, and is not already a member of another political party, other than Green Parties abroad, subject to clause 4(vii) below."

"No member of the Party may be a candidate for any other party in an election for any level of government and no member of another party may be a candidate for The Green Party in any such election except in cases of joint candidacies. No member of the Party may stand as an independent candidate against properly selected Green Party candidate(s). No member may campaign for any candidate standing against a properly selected Green Party candidate."Conservative Party"open to all who share its objects and values and who undertake to be bound by this Constitution"