There’s a lot of theories doing the rounds about why Labour lost the general election. Some leadership contenders think it is about Iraq or not being tough enough on immigration or benefit fraud.

But from the vantage point of an MP who increased her majority in a south London seat with many voters of the type we lost nationally, I think they’re missing the point.

The real reason we lost is because we forgot why we won in 1997. That victory owed a lot to our connecting with people who wanted to do the best for their families and by their families.

My friend David Cairns MP says that as a party we could no longer understand why someone might want to build a conservatory. Such modest ambitions became an object of incomprehension at best, or derision at worst, for too many in our party.

Equally, we failed to connect with the working parent who wants a decent school for their child, when we allowed the Tories to hijack academies as their own. And we lost touch with proud homeowners when we blurred our tough crime messages and tried to water down ASBOs.

We need to get back in touch with the aspiring classes who were the backbone of our support in previous elections and turned their backs on us in too many constituencies in 2010.

Credit where it is due: Gordon Brown did a good job rescuing the banks and tackling the global financial crisis. The mistake the party made was thinking that was enough to win a fourth term.

People were never going to vote to thank us for saving their savings. That’s what they expect from governments. People want more: they want hope for the future, they want a government that’s on their side, attuned to their aspirations. As a party, we forgot that basic insight. And we paid the price at the polls.

What aspirational voters didn’t want was an establishment party that offered more of the same, that had run out of ideas and was scared to venture outside its own comfort zone. We tried to justify the status quo rather than being warriors for change.

People want a better life for their children than they have had themselves. They don’t all want or expect their children to work in financial services or as lawyers. But they do want their children to have a job.

I know services are increasingly important to any developed country. And we need to be innovative in how we deliver them, ensuring they provide employment.

I also know that globalisation has driven many companies to lower wage economies in Eastern Europe and Asia. But there is still huge potential in specialist manufacturing. We boosted the NHS and schools, but did little to expand industries that could develop their equipment or machinery in this country.

And whether it is in services or manufacturing, we didn’t do enough to give young people the chance to develop practical skills through hard-edged employer-based apprenticeships – particularly important to those who don’t want to go to university.

This is the challenge for our next Labour leader: stop looking back and start looking forward. Leave the historians to analyse the past. We need to embrace and shape the future.

Our next leader needs to provide the aspiring classes with a sense that we share their hopes and understand their ambitions. I think David Miliband is best placed to do that. But whoever wins must offer a practical but radical sense of how Labour can meet the aspirations of those voters that we lost in 2010.

America is starting to come out of recession with more self-employment and more manufacturing. We need a similar drive on jobs and small business here: cuts may be inevitable, but they are hardly going to drive growth in themselves.

At our best, we can drive the reform and restructuring that’s needed; at our worst, we just protest the cuts without discrimination while offering no alternative. We have a choice: we need to decide which party we are. Our decision will decide our fate and that of those we should represent.