All voters get chance to take part in UK-wide polls in 2016
Voters across the whole of the UK will be able to go to the polls at least once in 2016 - twice if the referendum on EU membership takes place during the year.
A large set of diverse elections on Super Thursday on May 5 will give some 47 million registered voters the chance to vote in an unprecedented combined event just 12 months after the general election.
The polls cover: Scottish Parliament; Welsh Assembly; Northern Ireland Assembly; London Assembly; London, Bristol, Liverpool and Salford mayors; 124 English councils; and 41 police and crime commissioners in England and Wales.
To add to the complexity, four different voting systems will be in use: first-past-the-post (FPTP) for English council elections; FPTP plus proportional representation (PR) regional top-up seats for parliamentary or assembly polls in Scotland, Wales and London; supplementary voting (SV) for mayoral and police elections; and single transferable vote (STV) for the Northern Ireland Assembly.
If the elections are followed by the EU in-out referendum during 2016 it would mean that all registered voters will have been able to vote four times across the entire UK in the space of less than three years. Starting with the Euro elections in May 2014, followed by the general election in May 2015, the UK electorate then faces the diverse elections of May 2016 and the EU referendum that must take place before the end of 2017 but is expected in 2016.
The main reason next May's combined elections are so all-encompassing and without precedent is the police and crime commissioner polls, covering the 41 police force areas in England and Wales outside of the Metropolitan Police.
It will be only the second time the police elections have taken place. The first time was in November 2012 after the new police commissioner role was created. Those polls were mired in controversy over a low turnout and a lack of information for voters. Two subsequent by-elections have failed to inspire the voting public, recording low turnouts.
Another factor is that the London Assembly elections, last held in May 2012, coincide this time with those for Scotland, Wales and Northern Ireland, last held in May 2011.
The focus of attention in the May 5 polls will be the performance of the main parties in their first major test since the general election.
Labour, under its new left-wing leader Jeremy Corbyn, will face close scrutiny. Despite recent divisions and trailing in opinion polls, the party scored a solid win in the Oldham West & Royton by-election on December 3 when it held the Commons seat with an increased vote share.
I t generally has been holding its own in English council by-elections but faces a battle on May 5 when its control of perhaps a dozen councils may be challenged. The party will be under pressure from the SNP in Scotland, following the Scottish Nationalists' landslide north of the border last May.
The question for the Tories will be whether they can continue to build on their surprise general election victory. The Conservatives have established a lead in opinion polls and have done well in English council by-elections, gaining twice as many seats as they have lost.
The Liberal Democrats have seen some council by-election successes since they were reduced to just eight MPs last May. They will be seeking to show they can climb back from their massive defeat then.
Ukip, which won nearly 4 million votes but held only one seat at the general election, has seen falls in the party's vote shares in council by-elections. It came a distant second at the Oldham West & Royton by-election and has lost its majority on Thanet District Council owing to defections after dramatically taking control of it in last May's local elections.
As Nigel Farage's party focuses on the forthcoming EU referendum, its fortunes in the elections next May will be watched keenly.
The Greens' performance will also be under scrutiny after it received more than a million votes at the Westminster poll and held only one seat.
The SNP failed to win the Scottish independence referendum in September 2014 but made sweeping gains at the general election, leaving Labour, Lib Dems and Tories with just one MP each north of the border.
Since then the SNP has continued its onward march with swings in its favour in nearly all Scottish council by-elections that have taken place. The key question in May will be whether the party can increase its current slight working majority to dominate the Scottish Parliament and by how much.
The SNP is expected to do well in the 73 FPTP constituencies but the results from the 56 regional PR top-up seats should determine the outcome.
Plaid Cymru failed to make headway at the general election when it held three seats and will be under pressure to advance in the Welsh Assembly elections. Labour currently governs Wales as the largest party, with half of the 60 Assembly seats, and will be seeking a majority.
An early Northern Ireland Assembly election loomed after a crisis erupted at Stormont in the summer over the alleged involvement of Provisional IRA members in the murder of a Belfast man. However, a recent settlement between the parties means that the polls should take place on May 5 as planned.
The DUP will go into the elections under new leader Arlene Foster after Peter Robinson stepped down as party leader and as Northern Ireland First Minister following the agreement.
The Northern Ireland Assembly election could come just weeks after a general election in the Republic of Ireland due in the spring, in which the current Fine Gael and Labour coalition will be hoping to return to power.
Sinn Fein, contesting both polls, will be aiming to improve on the 14 seats it won in the Dail elections in 2011 while Fianna Fail, punished severely then over its record in government presiding over an economic crisis, will be seeking to recover.
The London mayoral contest to replace Boris Johnson, now Tory MP for Uxbridge & Ruislip South, is expected to be keenly fought, with issues such as housing and Heathrow airport expansion at centre stage. Prospective candidates who have been selected so far include Richmond Park MP Zac Goldsmith for the Conservatives and Tooting MP Sadiq Khan for Labour.
Following successes for Labour in London at the general election, the battle between Labour and the Conservatives in the capital's mayoral and assembly polls will get close attention.
The set of UK-wide May elections is expected to see controversy over "disappearing" voters, following the Government's decision to end the transition from household to individual electoral registration (IER) this month.
Mr Corbyn used his first party conference speech as Labour Leader in September to highlight claims two million voters could be removed from the electoral register and to accuse the Tories of trying to gerrymander the May polls. He urged a campaign to get people to register to vote.
The Government has defended the decision to finalise the IER change in time for the May polls, saying it will remove "phantom voters" and reduce electoral fraud.
The EU in-out referendum, when it comes, has been billed as a "once in a generation" opportunity for voters to decide the UK's relationship with the EU. It will see referendum votes counted overnight in 380 council areas across Britain plus one voting area for Northern Ireland and one for Gibraltar - 382 areas in total.
The referendum question on the ballot paper has been set as: "Should the United Kingdom remain a member of the European Union or leave the European Union?" The response options for voters will be: "Remain a member of the European Union" or "Leave the European Union".
The final outcome will be announced in Manchester by Electoral Commission Chair Jenny Watson as Chief Counting Officer for the referendum.