There are 31 parties putting up candidates for the European elections in Britain on 22 May. Some are well known, others less so. Here's a guide to all of them, beginning with those who already have a Member of the European Parliament:

Conservative

Media playback is unsupported on your device Media caption Prime Minister David Cameron: "Whatever it takes I will deliver that in out referendum"

Prime Minister and Conservative leader David Cameron said he had a track record of delivering on Europe at the launch of his party's campaign. On the party website, the Conservatives are focusing on their pledge to hold a referendum in 2017. Candidates: Fielding candidates in every region of Britain. 2009 result: 27.7% of votes, 25 MEPs elected

UK Independence Party

Media playback is unsupported on your device Media caption Nigel Farage predicts that his party "will win a seat" for the first time in Scotland in the European Parliament elections

UKIP leader Nigel Farage predicted "an earthquake" in politics at his campaign launch. The party, which wants the UK to leave the EU, is focusing on its website on the impact of being in the European Union on control of the UK's borders. Candidates: Fielding a full slate of candidates in every region of Britain. 2009 results: 16.5% of votes, 13 MEPs elected

Labour

Media playback is unsupported on your device Media caption Ed Miliband talks about "inequality and the cost of living crisis"

Ed Miliband promised to campaign for change within the European union as he launched his party's election campaign. On its party website, Labour says its MEPs will put "jobs and growth" at the heart of the EU. Candidates: Fielding candidates in every region of Britain. 2009 result: 15.7% of votes, 13 MEPs elected

Liberal Democrats

Media playback is unsupported on your device Media caption Vicki Young speaks to Nick Clegg as his party launches its campaign

Nick Clegg pitted his party's "optimism and openness" against the "fears and falsehoods" of "isolationists" at the launch of the Liberal Democrat campaign for the European elections. On the party website, the Lib Dems say the "fight is on" to keep the UK in the EU. Candidates: Fielding candidates in every region of Britain. 2009 result: 13.7% of votes, 11 MEPs elected

Green Party of England and Wales

Media playback is unsupported on your device Media caption Natalie Bennett says electors are turning to the Green Party whose councillors are "in it for the long-haul"

At the launch of the Green Party of England and Wales campaign, leader Natalie Bennett said the party would continue to "make a real difference" on issues like bankers' bonuses and fishing policy. On its party website, the Greens say European policy "does not need to be a shouting match" between extremes. Candidates: Fielding candidates in England and Wales. 2009 results: 8.6% of votes, two MEPs elected.

Scottish Green Party

Media playback is unsupported on your device Media caption Patrick Harvie said a vote for Scottish Green party would "send a message about the kind of country it wants to be"

The Scottish Green Party is hoping to beat the Liberal Democrats to sixth place in Scotland, claiming the constituency's final available seat in the European Parliament. The party backs a Yes vote in September's independence referendum and is campaigning for more power to be handed to local communities and better public services, according to their website. Candidates: Scotland only. 2009 result: 7.31% of vote, no MEPs elected.

British National Party

Media playback is unsupported on your device Media caption BNP's Nick Griffin: "We want to leave Europe immediately, without negotiations"

The BNP wants the UK to withdraw from the EU, while maintaining trade-based co-operation with other European countries. On its website, the party says it is the true patriots of British politics. Candidates: Fielding candidates in every region of Britain. 2009 results: 6.2% of vote, two MEPs elected.

Scottish National Party

Media playback is unsupported on your device Media caption Nicola Sturgeon accuses Chancellor George Osborne of "bluff and bluster" for continuing to rule out a currency union with an independent Scotland

The SNP promised to "ensure that Scotland's interests are always defended" in Brussels at its campaign launch. On its party website, it says Scotland needs a "seat at the top table" to make its voice heard. Candidates: Fielding candidates in Scotland only. 2009 result: 29.1% of votes in Scotland, two MEPs elected.

Plaid Cymru

Media playback is unsupported on your device Media caption Plaid Cymru leader Leanne Wood is "perfectly relaxed" about a referendum on Welsh membership of the European Union

Skilled migrants from other countries should be targeted to move to Wales, Plaid Cymru said as it launched its manifesto. On its party website, it says it will campaign for Welsh to be given the same status as other languages within the EU. Candidates: Fielding candidates in Wales only. 2009 result: 18.5% of votes in Wales, one MEP elected.

Here are the parties hoping to secure their first MEPs, listed in order of the number of candidates they are fielding:

English Democrats

Media playback is unsupported on your device Media caption English Democrats chairman Robin Tilbrook says the people of England are "waking up to the idea of being English".

The English Democrats launched their campaign pledging to "look after English interests" and arguing it was unfair to charge English people for prescription charges and tuition fees when these are free for residents elsewhere in the UK. On its party website, it points out the launch took place on site of the 1381 Peasants' Revolt. Candidates: Fielding candidates in every region of England.

An independence from Europe

Media playback is unsupported on your device Media caption An Independence from Europe's Mike Nattrass: "We are not the same, we are to the left of UKIP"

The party is pledging to take the UK out of the European Union without a referendum, to scrap VAT and build stronger links with the Commonwealth. It describes itself as an inclusive, democratic, Euro-realist, party on its website. Candidates: Fielding candidates in every region of England

No2EU - Yes to Democracy

Media playback is unsupported on your device Media caption EU is 'undermining democracy' says Brian Denny of No2EU

The party wants to hold a referendum on EU membership as a prelude to leaving the union. On its party website, it says it opposes privatisation and campaigns for workers' rights and decent public services. Candidates: Fielding candidates in the east and north-west of England, London, the West Midlands, Yorkshire and the Humber, Wales, and Scotland.

Christian Peoples Alliance

Media playback is unsupported on your device Media caption Christian People's Alliance Sid Cordle: "A lot of Christians believe that God is angry over gay marriage, and God can show that anger"

On its website, the party says the EU must be reformed to reflect the "Christian vision" of its founders and unless this happens, the UK should seek to leave. Candidates: Fielding candidates in the east and south-east of England, and London.

Socialist Party of Great Britain

Media playback is unsupported on your device Media caption Danny Lambert: "We are the most democratic organisation you will find in the world"

On its website, the party says it will be campaigning for common, democratic ownership of public services, the abolition of property rights and an end to inequality. Candidates: Fielding candidates in south-east England and Wales only.

Britain First

Media playback is unsupported on your device Media caption The leader of Britain First explains how he and "hundreds and others" left the BNP to set up their own party

On its website, the party promises to promote a "robust and confrontational" message about the need to leave the European Union, end immigration and put British workers first. Candidates: Fielding candidates in Scotland and Wales only.

Peace Party

Media playback is unsupported on your device Media caption Other parties have defence and military policies "tucked away in their manifestos", says the Peace Party

The party supports the UK's continued membership of the the European Union, which it says is a "force for peace", but urges the EU to be more pro-active. On its website, it also calls for a living wage and all foreign troops to be withdrawn from Afghanistan. Candidates: Fielding candidates in south-east England only.

Animal Welfare

Image copyright www.idjphotography.com

The party is campaigning for EU subsidies to be redirected away from livestock and fisheries farming into plant-based agriculture. On its website, it lists its other objectives including promoting healthy, plant-based lifestyle initiatives through public health and education campaigns. Candidates: Fielding candidates in London only.

Communities United

Image copyright Communities United

On its party website, Communities United says it is campaigning for reform of council tax and business rates and a university education for all. Candidates: Fielding candidates in London only

4 Freedoms

Media playback is unsupported on your device Media caption The top priority for the 4 Freedoms Party in European elections is to "create a new Europe", says leader Dirk Hazell

The party is vowing to give London a "strong voice" within the EU. On its website, it commits to aligning its MEPs with the European People's Party, the largest grouping in the European Parliament. Candidates: Fielding candidates in London only

National Health Action Party

Media playback is unsupported on your device Media caption Candidate Dr Louise Irvine explains the NHA plans to stop "privatisation and running-down of the NHS"

The NHS should be exempt from a proposed new free trade treaty between the European Union and the United States and food regulation should be strengthened, the party says on its website. Candidates: Fielding candidates in London only.

National Liberal Party

Media playback is unsupported on your device Media caption Dr Yussef Anwar on National Liberal Party policies

If elected, the party says its MEPs will consult constituents through social media and petitions before deciding how to vote on key issues. On its party website, it says its MEPs will also donate part of their salaries to good causes. Candidates: Fielding candidates in London only.

Socialist Equality Party

Media playback is unsupported on your device Media caption The Socialist Equality Party stands in Thursday's elections "on a history of struggle", says candidate Chris Marsden

The European Union should be replaced by a United Socialist States of Europe, the party says, with "workers' governments" and an end to the "age of austerity". On its party website, it says it is aligned with its sister party in Germany, Partei Für Soziale Gleichheit. Candidates: Fielding candidates in north-west England only

We Demand a Referendum Now Party

Media playback is unsupported on your device Media caption Nikki Sinclaire MEP says she would not not let David Cameron renege on his referendum promise.

At its launch, the party said it had just one policy, to force a referendum on EU membership. On its party website, it says the debate must be settled "once and for all". Candidates: Fielding candidates in the West Midlands only.

Europeans Party

Media playback is unsupported on your device Media caption Nigel Farage should be prosecuted, says Tommy Tomescu

On its party website, the Europeans Party says it is committed to promoting the UK's national interest within the EU and fighting "prejudice and discrimination" based upon nationality. Candidates: Fielding candidates in London only.

Harmony Party

Image copyright PA

On its party website, the Harmony Party describes itself as "ready and willing to remedy the inequalities of the current system of governance where the UK and Europe are concerned." It is fielding candidates under the slogan "zero immigration, anti-EU, pro-jobs". Candidates: Standing in the East Midlands, West Midlands, London, and south-east England only.

Socialist Labour Party

Image copyright Christopher Furlong

The party, led by Arthur Scargill, advocates withdrawal from the EU so the UK can "regain control of its economy, sovereignty and political power". On its party website, Mr Scargill says British farmers are "being paid not to produce food" at a time of worldwide shortages. Candidates: Fielding candidates in Wales only.

Liberty GB Party

Image copyright Liberty GB

On its website, the party says it is campaigning for withdrawal from the EU, the repeal of existing EU laws, the abolition of the Human Rights Act and legislative guarantees for freedom of speech. Candidates: Fielding candidates in south-east England only.

Pirate Party

All institutions, including the EU, should be more transparent and accountable, the party believes. It also wants EU data retention and intellectual property rights directives to be repealed. On its party website, it claims there "is more to life than Nick vs Nigel". Candidates: Fielding candidates in north-west England only.

Yorkshire First

On its party website, Yorkshire First says it is campaigning for a stronger voice for the region in national and European politics and more devolution, including a Parliament for Yorkshire. Candidates: Fielding candidates in Yorkshire and the Humber only.

YOURvoice

Image copyright YourVoice

On its website, YOURvoice is pledging to deliver "a better democracy". It states that constituents will be able to vote online to directly influence how its MEPs represent them in the European Parliament. Candidates: Fielding candidates in south-east England only.

Roman Party

Image copyright PA

The party, the brainchild of bus driver Jean-Louis Pascual, campaigns for an end to injustice and greater educational opportunities - as well as increasing knowledge of the Romans' contribution to modern Britain. It does not have a website. Candidates: Fielding one candidate in south-east England only.

A separate system is in place in Northern Ireland. More details on the candidates.

Here is a full list of candidates standing across the UK.