A guide to hung parliaments

Last week's election broadcast by the Conservatives is one of the most unusual to grace any campaign in living memory. We are accustomed to politicians attacking the policies of other parties, or the personalities of rival leaders – but this one was dedicated to attacking a theoretical possibility: a hung parliament.

For David Cameron, a hung parliament would be the crashingly disappointing end to four years of planning and hard work that were supposed to take him into Downing Street at the head a Conservative government in firm control of the House of Commons. Hence the series of grim warnings from the Conservatives that a hung parliament would mean weak government, which would aggravate the grotesque economic problems that the next administration will have to tackle. No one will benefit, according to David Cameron, except the politicians, who will love having the power to haggle and paralyse the government.

But none of the other parties is giving out the same fire and brimstone warnings – certainly not the Liberal Democrats, whose leader, Nick Clegg, could emerge from this election as the most powerful Liberal in British politics since David Lloyd George. Ed Balls, admittedly, argued that coalition government was not "the British way of doing things", but more senior party figures have insisted that that if there is a hung parliament, then, in Gordon Brown's words, "we've got to deal with it."

As for the voters, in their current anti-politician mood, they have by no means accepted the argument the a hung parliament is to be feared. On the contrary, many people find the prospect rather appealing.

But what would such an outcome involve in practice. If it looks as though neither Labour nor the Conservatives are going to reach the magic number of (theoretically) 326 seats – the number required to secure a majority – then you might want to bear in mind the following 10 points about hung parliaments.

What is a hung parliament?

This term is used loosely as if it describes a single phenomenon, when there is a whole range of possibilities that come under this heading. On the present boundaries, there are 650 parliamentary constituencies in the United Kingdom. At the last election, five were held by Sinn Fein, whose representatives refused to be sworn in as MPs. There is also the Speaker, and three deputy speakers, who by tradition do not vote. So, assuming no change in the Sinn Fein contingent, there will be 641 voting MPs in the new Parliament. If the biggest party in the Commons has 320 MPs or fewer, and the other parties in combination have 321 or more, it is a hung parliament.

What happens on 7 May?

Although we now have no MPs until the election is over, we still have a Prime Minister in Gordon Brown. Even if Labour comes third in the election, he will continue to be Prime Minister until someone else gets the summons to the Palace. Convention would dictate that he will get the first chance to try to put together an administration, even if his party has fewer seats or votes than its main rival. However, in an interview with the Independent yesterday, Mr Cameron hinted he would defy convention by forming a minority Government should he fail to secure a majority. "There is convention and there is practice and they are not always quite the same thing," Mr Cameron said.

There has only been one general election since the war which produced a hung parliament. That was in February 1974, when the Conservatives emerged from that with fewer MPs than Labour, but the incumbent Tory Prime Minister, Edward Heath, clung on in office while he tried to do a deal with the Liberals. He resigned only after the Liberals had turned him down.

And after that?

Almost anything could happen in this election, but Gordon Brown surviving as Prime Minister is one of the least likely of the possible outcomes, because Nick Clegg has said that he will not deal with him – although he might deal with the Labour Party under a different leader. If or when Gordon Brown goes, it would then be up to the Queen to send for the politician who has the best chance of forming a government. This is usually taken to mean the leader of the largest party, who is likely to be David Cameron, but it does not have to be. If Nick Clegg were to do a deal with, say, Alan Johnson, the Queen's advisers might tell her to call one of those two men to the Palace.

Would Nick Clegg keep Labour in power?

Despite all that has been said about a hung parliament, no one can know what will happen until the results are in. If the Conservatives receive more votes than any other party, and emerge with more MPs, it a safe bet that the next government will be Conservative. And if they are only a tiny number of votes short of a majority, David Cameron might even avoid trying to strike up an agreement with Nick Clegg, and rely instead on the Ulster Unionists. But if he is a long way short, he will have to talk to Clegg.

What kind of deal might David Cameron do with Nick Clegg?

On the ConservativeHome website last week, the retiring Tory MP Paul Goodman set out a whimsical scenario in which Clegg was appointed Deputy Prime Minister in a Tory-led coalition, with Vince Cable as Chancellor. This is bordering on fantasy. In reality, David Cameron may have to offer the referendum that the Liberal Democrats want on electoral reform as a price for taking office, but that is the most Nick Clegg can realistically expect. Cameron's authority in the Conservative Party will be seriously undermined if he fails to lead them to outright victory, and any deal with the Liberal Democrats will store up more trouble in his own party.

Will Nick Clegg then be Leader of the Opposition?

The position of Leader of the Opposition is an official one, carrying a big salary and other personal and political advantages. This has never caused problems before, because politics has been so completely dominated by the two main parties since 1945. However if the Liberal Democrats were to collect more votes than Labour but have fewer MPs, and David Cameron were to become Prime Minister, there would be a fine constitutional row about who ought to be opposition leader. The conclusion would probably be that it would have to be the leader of the larger party, meaning Labour. But the LibDems would be unlikely to take this quietly.

Will there be another general election in the autumn?

After the February 1974 general election, there was another in October in which Labour secured a small overall majority. This has led to an assumption that if there is a hung parliament this time, there will be another election within a year. However, in 1974, public opinion was against uncertainty, which meant that the Labour Prime Minister, Harold Wilson could call an election knowing it would go his way. Now, people seem to like the idea of what some call a "balanced" parliament. So if David Cameron is Prime Minister, he may have nothing to gain from a second election. On the other hand, the other parties may pass a vote of no confidence to force him to call one.

Would a hung parliament be democratic?

There are three main arguments against a hung parliament. One is that it is undemocratic. The argument goes that in a decisive election, the winning party puts a manifesto in front of the voters, gets a mandate from them, and is then required to fulfil all its manifesto promises; but in a hung parliament, those commitments are traded away as the parties do deals to form a government.

This argument overlooks the fact that every British government since the war has been a minority government, so there has never been a political manifesto that has been endorsed by the majority of voters. And the argument is weaker than usual in this unusual election, when everyone knows that the next government will have to take drastic measures to reduce the deficit, but no party is clearly telling the voters how they will do it.

How would the markets react?

It is also being suggested that the markets will react badly to a hung parliament because markets hate uncertainty. So far, there is no solid evidence of that. Some analysts think that what would really set off a bad market react would be a strongly entrenched government that appeared to be going about reducing the deficit in the wrong way.

Would a hung parliament be a disaster?

The other line against a hung parliament, which has been pursued vigorously by the Conservatives, is that it would lead to weak government at a time when the economy desperately needs firm handling. Yet Germany has one of the best managed economies in the world, and a system of proportional representation which invariably produces what we would call a hung parliament. Israel, which has also had a series of hung parliaments, is criticised for many things, but not for having for producing weak, indecisive governments. As a commentator in the Financial Times recently put it: "The Conservative objection is not a hung parliament per se. Were there a real prospect of Mr Brown winning an overall majority, Mr Cameron would be batting as vigorously as is Mr Clegg for an inconclusive result."