Q&A: What is a hung parliament?

Recent opinion polls have suggested a growing possibility of there being a hung parliament after the general election.

If it is to be avoided, either Labour will have to improve significantly on their current showing in polls, or the Conservatives will have to achieve one of the biggest electoral swings ever seen.

But since World War II, there has only been one exception to the rule that in the UK we do not elect hung parliaments.

What are they and why do we not have them very often?

What is a hung parliament?

A hung parliament is one in which no party has an overall majority, which means no party has more than half of MPs in the House of Commons.

It means that the government will not be able to win votes to pass laws without the support of members of other parties.

At the next election the number of seats contested will be increasing from 646 to 650 as a result of boundary changes.

That means that on the face of it, an absolute majority would require one party to win 326 seats and that if no party won that many seats there would be a hung parliament.

In reality, it is not quite that simple because the speaker and his deputies, although members of parliament, do not usually vote.

Also, in the current parliament, there are five Sinn Fein MPs who refuse to take the oath of allegiance to the Queen and as a result are not entitled to vote.

But in the simplest terms, the Labour Party will lose its absolute majority if it loses 24 seats and the Conservatives will gain an absolute majority if it gains 116 seats. Any result in between will result in a hung parliament.

What happens if there is a hung parliament?

The incumbent Prime Minister will remain in power until he or she resigns and may try to stay in government even if his or her party did not win the largest number of seats.

In 1974, Edward Heath stayed in power for four days after the election trying to put together a coalition, even though Labour had the largest number of seats in Parliament.

A party can stay in power without an absolute majority by trying to forge an alliance with a smaller party to create a coalition government, which would usually involve policy concessions and allowing members of the smaller party into the cabinet.

In some countries, instead of forming coalition governments, they have reached agreements with smaller parties that they will support the government if there is a vote in parliament aimed at bringing down the government and forcing an election.

Another possibility is for the biggest party to form a minority government with no agreements with other parties and just try to form majorities in favour of each individual bill as it comes up.

If no party is prepared to go down one of these paths then parliament will be dissolved again and there will be another election, although in effect that is relatively unlikely to happen because two elections so close together would be unpopular and the result would probably the same.

Has this happened in the UK before?

In the first of the two elections in 1974 there was no outright majority.

Labour won 301 seats compared with the Conservative Party's 297.

Harold Wilson formed a minority government, but it did not last for long, with another election in October 1974 giving Harold Wilson a slim majority of only three seats.

There was also a hung parliament following the 1929 general election, with Ramsey MacDonald's Labour Party winning 287 seats to Stanley Baldwin's Conservatives' 260 and David Lloyd George's Liberals' 59.

Occasionally, parliaments have also become hung parliaments in the middle of a session as a result of by-elections, as happened to John Major's Conservative government in 1996.

But that still means there have only been a handful of hung parliaments in the UK.

The BBC's David Dimbleby looks back to February 1974 - the last time an election produced a hung parliament

Other countries seem to have loads of them. Why don't we?

British politics has traditionally been dominated by two parties, although there is evidence of a shift away from that.

Part of the reason for the two-party dominance is the electoral system.

Israel has one of the purest forms of proportional representation. All voters choose from a list of parties, and parties get seats in the Knesset based on the number of votes they receive in the whole country.

That encourages single-issue parties and parties appealing to only one section of the population and makes it almost impossible for a single party to win a majority of seats.

After an election, the biggest party has to try to form a coalition with as many smaller parties as it takes to achieve a majority.

The UK is at the other extreme. A party will only win a seat if it gets the largest number of votes in a single constituency.

That means that parties have to try to appeal to as much of the population of individual constituencies as they can.

Smaller parties can win thousands of votes around the country but still not win a seat.

The system makes it much more likely that a single party will win a majority.