The next Labour government will oversee the biggest boost in affordable housing in a generation by getting tough on developers and reforming planning rules, the party’s deputy leader has said. Angela Rayner, also the shadow housing secretary, said she wanted to “increase, not decrease” the number of affordable new homes built every year, after it fell 12% last year. The Conservatives’ overall national housing target of 300,000 a year – which they have failed to hit – should be the “benchmark” of what a Labour government would deliver, she said, adding that she wanted to exceed that number. Housing will be one of the key battlegrounds ahead of the election, expected next autumn, after Rishi Sunak failed to mention it once in his speech at the Tory party conference in Manchester last week. Housebuilding in England is due to fall to its lowest level since the second world war owing to government policies that threaten to dramatically slow development. The government has been mired in rows over reforming laws that protect the 10 million Britons who own their homes in a leasehold and millions more who rent, as well as over nutrient neutrality rules that prevent pollution from developments. In an interview with the Guardian before Labour’s annual party conference in Liverpool, Rayner said: “Sunak has given up. He didn’t push back on his backbenchers on planning reform, which he knows was needed. “Michael Gove has had to give billions of pounds back to the Treasury because he’s not been able to get the affordable homes plan working. They’ve decided that it’s in the ‘too hard’ box for them to do anything about it. Everyone is paying for it.” She added: “The whole housing market has been destroyed because we’ve had three decades of nowhere near enough social housebuilding. Labour will ensure we deliver the biggest boost to affordable housing for a generation. If we don’t crack the nut now then the situation is only going to get worse.” Under Labour’s plans, the party would prevent developers from “wriggling out” of their affordable housing obligations, known as section 106 rules, by setting up a new expert unit to give councils and housing associations advice to get the best deal during negotiations with property firms. It would publish guidance to prevent developers claiming that building more affordable homes was not viable, permitting them to challenge 106 rules only if there were genuine barriers to building homes. “We would expect to be pushing for more but obviously it depends on the development. But developers can’t get off the hook, they will still make money but we’ll be supporting local authorities to push for enough affordable housing. I would want to see that number increasing, not decreasing,” she said. Rayner said she was “not closing the door” on any option to increase the amount of affordable housing – such as buying up new stock, building new social homes and making it easier for councils to use receipts from right-to-buy sales, after significant discounts left them without funding to replace the homes. After Michael Gove’s levelling up department handed back £1.9bn – including £255m meant to fund new affordable housing in 2022-23 – because it struggled to find projects to spend it on, Rayner said Labour would “unlock” government grants so more could be delivered. The party would do this by allowing councils and housing associations to use a greater proportion of the grant funds they receive – currently capped at just 10% – on buying housing stock they would then rent out as affordable homes. They could also fund projects where there is higher demand. “We deliberately haven’t put a figure on it, but there are a number of levers we can pull to push that up. I would want to see a significant increase on the 10% that we’ve got currently.” A leasehold reform bill would be in Labour’s first King’s speech – if the Tories fail to deliver one of their own next month – after the government dropped plans to abolish the “feudal” system of leaseholds across England and Wales in May. Labour plans to adopt Law Commission proposals including making it easier for leaseholders to buy the freehold or extend their lease. “At the moment people are being completely ripped off and they feel that. The balance isn’t correct,” Rayner said. After the government’s flagship renters’ reform bill, which would end “no-fault” evictions in England, was again put on ice, Rayner said that if the Tories failed to get legislation on to the statute book, a Labour government would. “Renters feel like they’ve been fleeced and they’ve got no recourse, no protection,” she said. “The government keeps saying it’s going to do something about it, but they’ve not. It’s leaving people completely insecure.” The House of Lords, led by Labour peers, last month voted down government attempts to relax river pollution regulations to promote housebuilding. Gove wants to bring forward a new bill to scrap the so-called nutrient neutrality rules. Rayner rejected Tory claims that Labour was against housebuilding, saying that there was a “third way” through the problem. “They want people to believe that it is the environment or it’s the houses. It’s just not true. There’s other ways of doing it,” she said. Labour has proposed setting up a scheme to make sure developers properly mitigate nutrients – work they say is too expensive – so that building work can go ahead at the same time. Ahead of the party’s conference, Rayner reflected on how her relationship with Keir Starmer had changed since their sometimes bumpy start. “We’ve just grown as a couple,” she said, laughing. “It’s like any relationship. You just learn each other’s ways”. But it was not just the prospect of a Labour government that persuaded them to be more disciplined, she added. “From day one the one thing we’ve been in step with was that we have to get the party ready for government,” she said. “In fact, I would say that’s kept us together at difficult times.”