At the final day of their party conference, we heard a Labour leader making the strongest commitment to social housing in over three decades. In doing so, he is effectively going to war with some of the most powerful Labour councils.

Rent controls in cities, a tax on landbanking by big developers, and forcing slumlords to bring their homes up to scratch: in what was easily the best speech Jeremy Corbyn has made as party leader, the strongest section was on housing.

Within minutes, he moved Labour policy forward by miles. While the general election manifesto had been disappointingly slight on housing – especially when set against his rhetoric – these remarks change all that.

They also set Westminster Labour squarely against Labour local authorities. When Corbyn began, “After Grenfell we must think again about what are called regeneration schemes”, many Labour council leaders in the audience must have had a start. For decades, Labour councils, especially in London, have invited in big developers to “regenerate” public housing estates.

What follows fits a wearily familar pattern. Families are booted out of their homes, the bulldozers tear down publicly owned property, and on the ruins are erected hundreds of expensive flats and a risible number of “affordable” homes. The developer makes their mark-up, the council gets some loose change, and the Evening Standard has something to fill its property pages.

Everyone’s a winner – apart from those now deemed too poor to live in their former homes.

This is what the academic Paul Watt has termed state-led gentrification, and it applies to the giant Aylesbury estate in Southwark, Cressingham Gardens in Lambeth, Love Lane in Haringey, and the Ferrier in Greenwich. And on and on: the activist group Architects for Social Housing has identified 195 council estates in the 21 Labour-run London boroughs that have been through this process, are going through it, or are faced with it.

The result, as Corbyn put it on Wednesday, is “forced gentrification and social cleansing, as private developers move in and tenants and leaseholders are moved out”. He could have added: as tenants and leaseholders of Labour councils are turfed out by the party many of them have voted for all their lives.

In 2014, Sophie Robinson-Tillett and I investigated this process at the giant Woodberry Down estate in Hackney. We spoke to pensioners living in exile from their children, old ladies who had seen their communities ripped apart and their backyards turned into smack dens. In the process, the developer told us, it would provide 1,177 “affordable” homes. The number of social-rented homes would drop from 1,555 to 1,088. The London Borough of Hackney has 13,000 applicants on its housing waiting list.

Corbyn’s response is twofold: if elected to government, he will compel councils to ballot all tenants and leaseholders before any regeneration. Second, all tenants on a redeveloped site will be entitled to move back to the same estate, on the same terms and conditions. “No social cleansing, no jacking up rents, no exorbitant ground rents.”

Taken together, the two promises would form a huge deal for any council estate facing the prospect of redevelopment. Imagine! Not just gerrymandered consultations but an actual vote. Not just councillor promises but legally enshrined protection. Some regeneration schemes would be killed at blueprint.

But Corbyn’s words also matter now – because the leader is taking sides against his own municipal leaders. His remarks are almost certainly miles from the estate-renewal scheme Sadiq Khan (who this week claimed “I love Jeremy Corbyn. We all love Jeremy Corbyn”) is drawing up in London’s City Hall.

In Haringey, the Labour leadership is pushing ahead with a plan to shunt housing estates, school buildings, libraries and other public property into a £2bn private fund – despite the opposition of local Labour MPs, the local trade unions, constituency parties and even many Labour councillors.

The plan has sent the local Labour movement into a bitter civil war. Corbyn has effectively taken sides in that war – and it is against council leader Claire Kober.

Imagine how many times she and her lieutenants will now have to defend themselves against the words of their own party leader and against the policy of their own party.

Corbyn ended his short section on housing with a promise of more policy to come within a year. Good. I’d like to see more money made available to build social housing, and a reflection of how our crocked housing market reflects an equally lopsided national economy – in which nearly all the chips are placed on the capital.

But this is a big and bold move. It would have been hard to imagine Corbyn making it before this June, and the election that entrenched his leadership. And it is a sign that he and his team plan to use the new powers they have.