Housing providers are backing calls for Philip Hammond to relax planning laws in the Budget to address the UK's chronic housing shortage.
Writing to the chancellor, an influential group of housing associations urged Hammond to allow developers to extend the height of properties without having to secure planning permission.
Under the "build up not out" plan, championed by Tory MP John Penrose, developers would be able to increase a building's height so it matched the tallest building in its neighbourhood, or the height of surrounding trees.
The aim would be to produce mansion blocks, rather than towers, Penrose said, and would avoid the need to build on green belt land.
In a letter to the chancellor, housing associations G15, Placeshapers, Midland Heart, Orbit, and Place for People wrote: "We believe that, "build up not out" has the potential to substantially increase the supply of sites for development.
"We have the financial strength, the capability and the networks of local suppliers to be able to build greatly increased numbers of homes. Housing associations have an ambition to deliver."
Sam Bowman, executive director at the Adam Smith Institute, welcomed the proposal, saying it would boost productivity and growth.
"This would be a bottom-up way of making housing more affordable, allowing market forces to incentivise development in the places that people want to live most, and giving us more of the sorts of mansion flats and dense terraces that make up some of London's most liveable areas like Bloomsbury and Fitzrovia," he said.
However Bowman said the government must still consider building outwards by reclassifying green belt land, especially around train stations.
Melanie Leech, chief executive of the British Property Federation, said: "If we're going to deliver the housing numbers that we so badly need, it's critical that we find bold new ideas to increase supply.
"'Build up not out' is a good example of an initiative which should encourage local authorities to think creatively about solutions in their area."
Sajid Javid has been calling for radical changes to fix the housing crisis (Source: Getty)
Penrose first submitted the policy to communities secretary Sajid Javid's housing white paper, which was published in February, and has since held multiple meetings to drum up support for the idea with MPs.
Hammond has already rebuffed controversial "borrow to build" put forward by Javid which were supported by the property industry.
Javid suggested that the Treasury could take advantage of record-low interest rates to borrow billions to fund infrastructure projects which would unlock land for housebuilding.
However, Hammond responded by saying it would not be responsible for the Treasury to borrow more money.
A Treasury spokesperson said: "The chancellor is looking at a wide range of options ahead of the Budget, but anything more than that is pure speculation."
Meanwhile, Sadiq Khan also pressed the chancellor last night, asking for the Budget to devolve powers over public land to London. The mayor said councils must be allowed to borrow to invest in homes, and repeated Javid's demand for infrastructure spending.