I have always been motivated by a burning desire to tackle inequality and injustice, to stand up for the powerless against the powerful. That’s my socialism. If I see something wrong or spot an injustice, I want to put it right. It’s why I spent 20 years fighting the death penalty across the world, why I marched against the Iraq war, and why I defended the rights of victims of domestic violence as director of public prosecutions.

Today’s inequalities and injustices are obvious: a radical Labour government is needed now more than ever. Inequalities of every type – in power, education, health and wealth – have become ingrained in our society.

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A generation of children, including my own, have never known a time without homelessness on our streets. Our public services have been decimated by cuts, leaving schools begging parents for money, and sick patients in hospital corridors. The Tories’ assault on welfare has stripped people of their dignity. The future of our children is too often determined by where they are born, and their class, race and gender. We cannot walk past these inequalities and injustices.

Labour lost the election. But the moral fight against inequality and injustice must continue. We must lead that fight against a prime minister with no conviction or principles. Our arguments must be made in parliament, and we must also take them to the country – to the communities we lost at the election, whose trust we need to win back.

As we learn the lessons of our defeat we must relentlessly focus on the future. We can win again if we make the moral case for socialism, a moral socialism that is relevant to people’s everyday lives and the challenges we face as we move into the 2020s and 2030s. There are three foundations to this: economic justice, social justice and climate justice. I believe the free-market economy has failed. It leaves too many people behind, and has fuelled gross inequality. We should be arguing for a new economic model that reduces that inequality, supports trade unions, gives people a real voice in their workplace and enables communities to thrive.

The argument that something can be good for the economy but bad for the environment must end. If it’s bad for the environment, then it is bad for the economy. We are the party of the green new deal, and that must be hardwired into everything we say and do. Businesses, investors and consumers clearly have their role to play, but only a determined lead from government can make this happen. The UK can set an example that leads the world, but only if it is seen to be forging an international alliance to end the climate crisis.

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As we move forward, we must continue to be the party that opposes austerity, supports common ownership and champions investment in our public services. We need to properly fund and defend our NHS and to make the case for a social care system that tackles the scandalous neglect of older and disabled people.

We must argue for radical devolution of power to our nations, regions, towns and cities. Many people across the country are understandably frustrated because decisions are taken about them, without them. We need to break the grip Westminster has over our politics and put decisions in the hands of our communities.

There are two parts to being Labour. First, enabling everyone to get a decent education, the best job they can, better standards of living and a fulfilling life. The free market has failed in this endeavour. We have to fight to put wealth, power and opportunity in the hands of all.

The second part is just as important. People’s lives don’t always work out the way they want. I have seen this at first hand in all the work I have ever done. Labour should always stand by people. The social security system should be decent, strong and unbreakable, with dignity at its heart. That’s what being Labour means.

You can’t tackle injustices, right wrongs or change lives if you don’t win elections. I’m standing to be leader of the Labour party because I want to win. Endless Tory governments are not inevitable. Another future is possible, but we have to come together as a party and as a movement to fight for it.

Labour’s values are my values: peace, justice, equality and dignity for all. Labour can win the next election if we hold true to those values, unite as a movement and focus with confidence on the future. And when we win, it will not be for ourselves, it will be for all those communities who need us now more than ever – and everyone who wants to live in a better world.

• Keir Starmer is the MP for Holborn and St Pancras and a candidate for the Labour party leadership