Yesterday we saw the worst set of public finance figures in our peacetime history. According to some forecasters Britain is set to have the largest budget deficit of any G20 country this year. It could be more than 10 per cent of our GDP – that is easily the biggest deficit since the Second World War, and worse than countries that have had to go to the IMF.

We can't put this problem off until some unspecified time in the future, however much this government would like to do so. Our fiscal position is sapping confidence, which means we are losing a potential cash injection into the economy that our indebted Treasury cannot afford itself. So that's why the Conservatives will make debt reduction a high priority. If we don't take concrete steps to start reducing this massive debt now the recession will get worse, and the recovery will be delayed. To achieve this we need to control public spending, in both the long term and the short term.

In the long term, we will control spending by reducing the demands that the broken society makes on the state. Family breakdown, welfare dependency, educational failure, addiction and crime all cost taxpayers untold billions a year. If we do not confront the root causes of these problems that bill is only going to rise. That's why far from retreating from our plans for school reform, welfare reform and strengthening families, we are as committed to them as we have ever been.

Download the new Independent Premium app Sharing the full story, not just the headlines

These social changes will not produce public expenditure savings in the short term, so we need a plan to control public spending now. The work to restore fiscal sanity will have to start on day one, in order to build the confidence of consumers and the international markets. That means examining each extension of the state that has taken place to see if it is delivering results. That means curbing the culture of excessive executive salaries in quangos. And that means assessing whether it is right that people who earn as much as £50,000 a year receive tax credits. But this doesn't mean we are going to behave like turbo-charged accountants, slashing spending without regard to the social consequences. We are going to behave like progressive Conservatives.

There will be tough decisions to make, and there will be people to disappoint – I would never claim that controlling public spending can be a pain-free process. But it is an entirely different exercise when it is underpinned by a clear and compassionate philosophy. Its objective is a society that is fairer, safer and greener, where opportunity is more equal – and where future generations aren't burdened by our debts.

If we are in government these objectives will be at the forefront of our minds every single day, leading each and every spending decision we make. Because today, my Party understands that fiscal responsibility needs a social conscience, or it is not responsible at all.

David Cameron is the leader of the Conservative Party