Labour lost the general election in May in the first few weeks after our defeat in 2010. If we’re not careful, we run the risk of making the same mistakes. It is that critical. I believe we can win the next election – but all depends on the choices we make now.

Two things are essential. First, we need to defend our record. It’s true that people do not vote for you on the basis of what you did in the past. But they do judge your character on what you’ve done. That judgment and perception will colour how people regard promises for the future.

I learned this the hard way, spending 18 years in opposition as an activist, a councillor and then an MP. While the party debated doctrine and ideology, the poorest pensioners saw their incomes fall, hospital waiting lists grew, school buildings decayed and our railways fell to bits. I could march all I liked, but children went to schools with 33 to a class, one teacher, no classroom assistants and outside toilets.

In government, I wrestled with delivering change for 13 years, from creating tax credits to modernising our railways and responding to the global financial crisis. It wasn’t always easy and no government is perfect, but we should be proud of what we achieved and should have defended it and recognised it more over the last five years. The NHS was turned around. Class sizes fell. Schools were rebuilt. The minimum wage the Tories now take pride in raising is our achievement. The centre ground is a good place to be.

Two weeks ago George Osborne was able to present a budget which, if it had been presented by a Labour chancellor, would have been howled down. For five years he trashed our economic record, which let him paint Labour as the party of tax and spend. Yet in his own budget he announced that he would spend more, borrow more, and tax more still.

Where were our arguments to counter the fallacies? We stopped recession becoming depression following the global banking crash. The economy was growing in 2010. Yet the blunt fact is that a majority of the public bought the Tory argument that a global crash was all Labour’s fault. We let our opposition get away with it.

That failure on our part hobbled us right up to polling day. No matter how many attractive promises you make, you won’t get a hearing if people don’t have confidence in your economic judgment. It was that essential truth that Gordon Brown and Tony Blair grasped in the 1990s and which provided a sound platform to campaign for a fairer and more just society.

It seems to me that we have three choices. We could collectively go out to lunch, as we did in the 1980s. We left the field to Margaret Thatcher, and the Tories enjoyed power for 18 years. Then there’s the easy option of hoping that in five years’ time the voters will have had enough of the Tories and come round to our point of view. Safety first is not going to work.

We have no right to exist: that has to be earned. We must rediscover our self-confidence and self-belief. But most of all that sense of purpose that took us into power in 1945 and in 1997.

To win, people must have confidence that we have the right answers and conviction to deal with the problems that will face the country as we enter the third decade of this century.

So the second challenge is to show how we have answers to a fast changing world. We are a big country and should have ambitions to match it.

We want people to get on, each generation building on the achievements of the last. That needs a strong stable economy, but also needs investment. Borrowing to provide housing or a decent transport system is a good thing and we should say so. Investing in universities and improving performance in schools is essential. And yes, we need to get debt and borrowing down, as I have always said. I’m glad Osborne was able to meet my target.

We also believe in building a fair society; to take one example, tax credits (which came from the US, no leftwing conspiracy there) support income for many who will not benefit from the minimum wage. We also need to be outward-looking, working in Europe though not afraid to criticise the lunacy of what’s happening in the eurozone and Greece today.

We must be ready to defend the solidarity that comes from staying within the United Kingdom. Remember: we won the referendum decisively as Nicola Sturgeon admitted only last week. Too many party members seem to have forgotten that. It was confidence and self-belief that won it.

As I reflect on all of this, I have to decide who to support as leader. So I will be voting for Liz Kendall, because I think she recognises the scale of the challenge we face. She is a realist, but also understands that if we are not the party of change we could easily become a party of the past.