Clegg has a real chance to change the system. He must not blow it

All three parties lost the election, but there was still a winner.

The Liberal Democrats performed poorly. There was no Cleggmania by the time voters headed for the polling stations. As far as the Liberal Democrats are concerned it should not matter. They have secured what is for them the dream outcome. The electoral system rarely delivers a hung parliament. This time it has. It will not do so again for a long time. Nick Clegg has the chance to seize the moment and get a change to the voting system. There is a danger he will let it pass – an error that is entirely in line with his party's tentative approach to the pragmatic demands of power.

Clegg declared in advance of the election that the party that secured most votes and seats should have the first chance to attempt to form a government. He was obliged to repeat his declaration yesterday. Some Liberal Democrats seem convinced that they will get credit at the next election by allowing the Conservatives to rule. They are deluding themselves. They risk being swallowed alive.

Of course they face a dilemma. The politics of power presents parties with nightmarish dilemmas every hour of the day. The Liberal Democrats are not used to the politics of power and this is a big test. They do not want to be seen propping up a Labour Party that by any definition performed abysmally in the election. For a time they will no doubt face a critical onslaught. Clegg hates the idea of appearing with Gordon Brown on the steps of No 10 having agreed a deal.

But they are being spectacularly naïve if they believe the formation of a minority Tory administration will lead to their party's revival over the next few years. Similarly, Labour figures who assume a period of opposition would give them space to form a new progressive alliance with the Liberal Democrats that will soon sweep them to power are also deluded. Once the Conservatives seize power they will not let go.

If David Cameron forms a minority government he acquires all the powers of patronage and crucially the power to decide when to call another election. The importance of these levers cannot be over-estimated. Although I have spoken to several senior Conservatives who are livid about their campaign and regard the outcome as a defeat, they will probably keep quiet in the near future. They want to be part of a government. New Tory MPs will arrive with a hunger for office that will be a form of discipline in itself. All of them will also know that a second election soon is highly likely. They feel mutinous but such are the stakes they will not undermine a fragile government that has the chance to become stronger at some point in the near future.

Cameron will call a second election when the Conservatives are well ahead in the polls. He will have every right to call one on the grounds of the need for political stability. The Liberal Democrats would be back to where they were before – irrelevant at a national level.

More immediately, a minority Conservative government would get a honeymoon as the Labour government did when Harold Wilson became Prime Minister in February 1974, the last time the current voting system produced a hung parliament. Wilson called a second election in October and won. Cameron will be in a stronger position than Wilson when he calls a second election. The Conservatives have the money and the media backing to win convincingly.

The alternative for Clegg to a deal with Cameron is no political paradise. It would be almost impossibly difficult to work with an unpopular governing party. And yet it is very straightforward. They would get a referendum on electoral reform this year. There is a strong chance the referendum would be won. The next election would be contested under a system that is fairer and the political landscape would change.

No doubt Clegg and others would prefer to secure the reform in a noble context, but there never is change when altruism is called for. Every constitutional reform has been implemented out of self-interest. No Prime Minister changes the voting system to do their party harm. They act out of party interest. Tony Blair did not give the Liberal Democrats a change in 1997 because he had won a landslide. They are being offered one now because Labour has lost its majority. Yesterday I heard a lot of talk about Labour and Liberal Democrats winning the case for electoral reform in opposition, securing power and then introducing the change. This is a fantasy. They must take the chance now or it will not happen.

If Clegg takes the alternative path he faces a few dilemmas as well. How will his party respond to his support for George Osborne's emergency Budget? There is a lot of discontent in the Conservative Party about Osborne this weekend. Some senior figures blame him directly for their failure to secure an overall majority. Is Clegg going to pay homage when some Conservatives privately fume?

Cameron's statement yesterday afternoon was perfectly pitched, highlighting areas were there is agreement between the two parties, or more precisely consensus between some in both parties, but the offer of a review on electoral reform is meaningless. Cameron will have called a second election long before the review is completed.

What will happen if Cameron becomes Prime Minister over the next few days? Brown will go quickly. Probably Harriet Harman will become acting leader while Labour stages a leadership contest. Cameron will navigate awkwardly, but I suspect with some skill, a balancing act in which he claims to be a liberal Tory while seeking to keep his restive right on board. This cannot be a rampant Tory government like the ones elected in the 1980s with landslide majorities. Clegg would struggle to keep his party united.

Hidden beneath the drama of the moment are deep divisions within each of the parties. Clegg's decision on what to do next will test the precarious unity of the Liberal Democrats. A Labour leadership contest will highlight suppressed tensions about the party's future. Some in the Conservative Party are ready to rage if power is not secured. But only Clegg and his party have the power to decide whether or not permanent change follows the most astonishing election of modern times. They have yearned for such a moment, but might turn away fearful of its political impurity. A pure moment is never going to arrive.