All new governments claim that they are governing for the long term. Most end up being pushed around by short-term events. All claim they have a plan. Most end up with no plan at all. All say they're going to ignore headlines. Most end up driven round the bend by the press.

So I understand why people might react with scepticism to the claim that, this time, this government will be different. But as this new coalition government approaches its first 100 days in office, I believe the claim is a strong one: we will govern for the long term and we'll stick to our plan.

There are two reasons why: first, the nature of coalition and, second, the scale of the economic challenges ahead. A coalition can only work if it is upfront about the differences between the two parties and explicit about the partnership it is seeking to create. It requires collective decision-making and a high level of candour as two different parties seek to govern together.

The fiefdoms, factionalism and backbiting of the Blair-Brown years thrived within the secretive world of internal Labour party politics. The differences between two parties in one government, on the other hand, are explicit and so in some ways easier to overcome.

That is what our painstakingly negotiated programme for coalition government was all about: a five-year plan for government based on a clear understanding of our differences and the nature of our collective strength. So we have had a much more radical first 100 days than conventional wisdom predicted, confounding the myth that compromising on policies means you are left with a bland, cautious mush, the common denominator approach.

Instead, we have set out radical steps to boost patient power and local democratic accountability in the NHS and steps to give more freedom to parents, teachers and communities in our school system, combined with more money for disadvantaged children. We are restoring a plethora of rights to liberty and privacy and have set out an ambitious programme for lasting political reform. And we have held an emergency budget, taking a big first step towards a fairer tax system and setting out plans to eliminate the bulk of Britain's enormous budget deficit.

That is not bad going, by any account. But the truth is that this government doesn't expect anyone to reach their verdict after 100 days. We expect to be judged on what we have achieved in five years. That should be a relief. When government lurches from one short-term goal to the next, the country pays the price. In their daily desperation to sound tough, Labour sacrificed one hard-won civil liberty after the next. Transfixed by gravity-defying profits in the City, they ignored the unsustainable bubble in Britain's housing market and refused to control the reckless irresponsibility of our banks.

Even at the bitter end, desperate to shore up their crumbling support, they kept on writing cheques they knew would bounce.

We have to play the long game. The depth of the economic difficulties we have inherited from Labour means there are no short-term fixes. The size of the deficit means that whichever party or parties had come into government would have to face short-term unpopularity in order to restore long-term success to our economy. Reducing public spending has already led to some controversial decisions and, with the autumn spending review approaching, we are on the brink of many more.

Getting the economy back on track is this government's priority; it will no doubt remain that way for our entire time in office. Setting out a bold plan on the public finances is unavoidable if we are to retain confidence in our economy, avoiding decades of debt, higher interest rates and fewer jobs. There is no social justice in passing on the dead weight of this generation's debts on to the shoulders of the next.

Our ambition is to leave a strong economy, rebalanced so that opportunities are spread across all of the country. Equally, sustainable growth must be built on a range of industries. We won't pin all of our hopes solely on a return to health in our financial services. We'll tap the enormous potential in British industry, manufacturing and R&D.

So far, this coalition government has confounded expectations. First, we were told the coalition agreement couldn't be done. Then we were told that the coalition government wouldn't work. Now we're told it won't last. We intend to confound expectations again. One hundred days? That's not the prize. It's the next five years that count.