Margaret Thatcher used to claim that New Labour was her greatest achievement. Her point was simple: you knew you had won when your opponent started using your arguments.

Her successor in Number 10, Theresa May, had until last week been a member of a government wholly committed to the expansion of the free market and the shrinking of the public realm. Margaret Thatcher promised to “roll back the frontiers of the state”. David Cameron oversaw the steepest cuts to public expenditure since the Great Depression. Theresa May now says that the Conservatives believe government is a “force for good”.

As May and her Chancellor try to lay out their new course for the economy, the rhetoric of helping the working class will not match the reality. You don’t help those who work by cutting the in-work benefits like tax credits that so many rely on. You don’t help those who work by cutting back on their workplace rights. The Tories may have changed their approach to the economy but the fundamental Tory values remain the same.

But this is the week that the rule of free market ideology ended in Britain. The argument on the economy has decisively shifted to the left. There will still be loud voices raised by some true believers on the Conservative side, perhaps enough to seriously destabilise a Prime Minister with a small majority. But the battle on the economy has been won by those on the left who stood for the values of community and fairness, and who argued that far from producing a fairer and more efficient society, the ideology of the free market had produced monstrous waste and inequality.

We now need to define what the future will look like. PM May has offered us one version of it. It is the 1950s without the optimism – a return to grammar schools with the added bigotry of foreign worker lists. As Jeremy Corbyn made clear, Labour will resolutely oppose any attempt by her government to blame its failures and the misery of a hard Tory Brexit on our migrant communities.

We know there are challenges ahead, in combating climate change, negotiating a Brexit that works for everyone, and tackling the grotesque levels of inequality in our country. But there are huge opportunities for us, too. Instead of the slow-burn environmental disaster of fracking, we should be making Britain one of the world’s leading renewables producers. We have huge natural resources in our wind and our waves that we should be putting to better use. We have an immense heritage of science and engineering expertise that we can draw upon. We have the potential to rebuild and transform our former industrial areas, in the green manufacturing renaissance, exporting the technology into a fast-growing global market. This needs a government committed to supporting the industry, with investment in renewable energy and scientific research.

Instead of taking small business and self-employed people for granted, Labour will build new regional development banks that can supply the patient, long-term investment our small businesses need to grow. And with our co-operatives and employee-owned businesses growing faster than the rest of the economy, we should be looking to support this new generation of business owners.

And we do not have to tolerate the continued unfairness of austerity. New Chancellor Philip Hammond does not have to continue with George Osborne’s choice to impose spending cuts. Labour’s Fiscal Credibility Rule commits it to shrinking the deficit without trashing public services or destabilising the economy. We can rebuild and transform our economy so that it is economically and environmentally sustainable, and fairer and more prosperous for all.