21 years ago yesterday I became leader of the Labour Party. A lot has happened since then. We discovered winning successively. And now we have re-discovered losing successively. Personally I prefer winning.

I could make a speech to you about how to win. You win from the centre; you win when you appeal to a broad cross-section of the public; you win when you support business as well as unions. You don’t win from a traditional leftist position.

But given the state of the debate in the Party right now, I don’t want to.

Because this plays into the single most debilitating feature of the current debate: that this is a choice not only between government and opposition, but between heart and head, between the pursuit of power and the purity of principle.

It isn’t. The choice is precisely about principle. It is about what support for our values means in the modern world.

Social democratic politics in the early 21st century has one great advantage; and one large millstone.

The advantage is that the values of our age are essentially those fashioned by social democracy. We live today in a society that by and large has left behind deference, believes that merit not background should determine success; is inclined to equality of opportunity and equal treatment across gender and race; and believes in the NHS and the notion at least of the welfare state. This doesn’t mean to say this is the reality. But even the Tories, in the open, have to acknowledge the zeitgeist.

What should give the Labour party enormous hope and pride is that we have helped achieve all this.

However, the large millstone is that perennially, at times congenitally, we confuse values with the manner of their application in a changing world. This gives us a weakness when it comes to policy which perpetually disorients us and makes us mistake defending outdated policy with defending timeless values.

We then misunderstand the difference between radical leftism, which is often in fact quite reactionary, and radical social democracy, which is all about ensuring that the values are put to work in the most effective way not for the world of yesterday but for today and the future.

So when our reforms produced declining waiting lists in the NHS or transformed much of London’s schooling or cut crime these weren’t a betrayal of principles but implementation of them. Betrayal would have been leaving a system of failure in place, even if we created such a system in an earlier time.

So let me make my position clear: I wouldn’t want to win on an old-fashioned leftist platform. Even if I thought it was the route to victory, I wouldn’t take it.

We should forever stand for social justice, for power, wealth and opportunity in the hands of the many not the few, as our constitution puts it.

But that is not the challenge. That challenge is: how to do it in the modern world.

And here is where the challenge deepens.

The most important characteristic of this world is: the scope, scale and speed of change. Change defines it.

Technology alone is a revolution with vast consequences for every sphere – business, public services, lifestyle and government. Globalisation is opening the world up, with attendant opportunities and of course risks. Individuals – partly through these changes – live quite differently, with infinitely more choice over their own life. Businesses grow and decline with bewildering speed, making a thriving entrepreneurial sector a necessity. Development of human capital becomes vital for the future economy. And the fallout from all this creates new problems – like social care for increased numbers of elderly – and new victims like those left behind or disadvantaged by the changes whirling round them.

This change requires new thinking. And 2015 is not 2007 or 1997. So yes, move on. But don’t move back!

If we do, then the public won’t vote for us, not because our thoughts are too pure but because they’re too out of touch with the world they live in.

So we should use defeat as an opportunity. We have to rebuild. But approached in the right way this is exciting not depressing. How?

We get thinking – about policy, real policy not one-liners which make a point (useful though those can be in a campaign). Technology and its implications for everything from the NHS through to government itself, is the single most important dimension. But across the board, from infrastructure to housing to tax reform to welfare, we should be thinking through new solutions framed against how people live and work now.

We need to regain economic credibility. There is a perfectly sound case for saying we should have tightened policy before the crash; there is absolutely no case whatever for effectively accepting that Labour caused it. But we cannot address the future unless we are clear about the past and unless we show we’re completely confident in economic policy.

Some forward-thinking Labour local councils have done great work. Celebrate them and learn from them.

Develop a dialogue with business about their challenges and needs; about productivity, skills and a modern industrial policy.

Work out what a political organisation looks like today: how we make decisions, how we communicate, how we get our message across. There is a wealth of example all over the world. We should access it.

The SNP and UKIP have clouded our sense of direction because they seem to point away from the centre. But our response should be likewise based on principle. The answer to the problems of Scotland is no more about being more “Scottish” and leaving the UK than the answer to the problems of England is being more “English” and getting out of Europe or blaming immigrants. So take them head on. I don’t know whether this is a winning strategy, but at least its one I believe in.

We won elections when we had an agenda that was driven by values, but informed by modernity; when we had strength and clarity of purpose; when we were reformers not just investors in public services; when we gave working people rights at work including the right to join a union, but refused unions a veto over policy; when we understood businesses created jobs not governments; and where we were the change-makers, not the small -c conservatives of the left.

We won not because we did what we thought was wrong as a matter of principle but right as a matter of politics; but when we realised that what is right as a matter of policy is right as a matter of principle.

Labour shouldn’t despair. We can win again. We can win again next time. But only if our comfort zone is the future and our values are our guide and not our distraction.