The UK is in the midst of a housing crisis. More people want a house than can afford to buy one, and in the rental market prices are out of line with salaries in many places. As a historian of cities and urban development, I'm taking a moment to consider what the problem actually is, and whether the suggested remedies will actually solve it.
More people want a house than there are houses available: basic market economics pushes the prices of houses up. In the UK the issue is also complicated by geography. There are empty houses, and properties languishing on the market. I'm not just talking about luxury flats in London owned by foreign investors (although this is perhaps part of the problem I doubt it's a large proportion). The unwanted houses are in towns where the mill or mine closed down decades ago and employment opportunities are few. So the problem cannot be framed as simply "UK needs XX,0000 new houses per year" when the demand is for houses specifically within easy reach of London (and to a lesser extent Birmingham, Bristol and Manchester). All these cities have brownfield sites that could be effectively converted to housing, and that is certainly something to be encouraged.
But there are further questions I don't see asked in most of the discussion of the housing crisis. The questions are as fundamental as what we think of as "normal" patterns of residence. One element is a culture that has emerged over generations and seems specific to English-speaking countries, of home-ownership as a prime means of investment and the owner-resident being the normative middle-class position. This has been encouraged by the state in various ways (for instance making mortgage interest tax deductible, which is no longer the case in the UK but still is in the US, and not counting primary residence for means-tested benefits). It is also encouraged more broadly in society, where long-term tenancy (except in social housing) is rare. Real estate is seen as a safe investment - and given the last few decades' massive price inflation on residential property it has definitely paid off for many. In fact, so entrenched has the idea become of homeownership as a retirement plan that lifetime tenancy is seen as a social problem (as it is not in, for instance, Germany or Italy).
This social focus on home-ownership as a standard life goal is part of the explanation for the housing crisis, but we need to also recognise changing social patterns of residence - and consider whether proposals to address the crisis will anticipate how society may change further.
The type of housing people want changes. Even a generation ago, it was normal for a middle-class family to have a 3 bedroom house, with one bathroom, and to raise a family in that space (and it was affordable for single-breadwinner families). The expectation of multiple bathrooms, a bedroom for each child, and the amount of personal space now considered "normal" in suburban residences only came to be seen as normal once it became affordable for a significant proportion of the middle class (notably, once households with two working parents also became standard).
This does not mean that the suburban tract is always the answer, though. The UK already has some traces of the larger problem in America, of unsaleable suburban houses, while millennials prefer to live in the city.
The proportion of the population living alone has also increased. This has shaped the development of new housing, with more studio and one bedroom flats, and in many suburbs the conversion of houses to multiple dwellings. But we don't know that this trend will continue. It is historically not "normal" for significant numbers of adults to live alone. It only became normal, again, once it became affordable for a large-ish cohort during a particular historical window.
In the early twentieth century, single adults in cities often rented a room from a family, or lived in residential hotels. In high-demand cities like London or New York, these would seem like an ideal answer to some of today's housing pressure, but the residential hotel is largely a thing of the past (as is the lodger). After the Second World War, such residential models dropped in popularity as people moved to the growing suburbs, and living in a residential hotel ceased to be seen as "normal". Meanwhile, cities imposed various laws to drive these housing types away, in the case of the hotels often in favour of more lucrative corporate development. But we must remember that the regulations only shut down the lingering elements of the residential hotel model already waning in popularity (most residents were elderly long-termers). Cities would not have been able to legislate successfully against a housing type that was still popular with a significant number of urban residents. Urban authorities could turn this around, particularly in the age of Air BnB, and offer ways for the residential hotel to become viable again - and perhaps again seen as normal.
For new development, the challenge is providing more housing which is both affordable and of a kind that people actually want. This may seem obvious, but the difference between the architecture people want and what they're offered can be stark.
What the UK could also work on is expanding transport infrastructure so that houses (currently empty) in smaller towns could be viable for commuters. The money being spent on HS2 could have been better assigned to reopening some branch lines, to towns that have been cut off from railways since the 1960s.
While the demand is there for more houses, I am not convinced that this can ever be fully addressed. This is cynical, but I suspect that much like Parkinson's law of tasks expanding to fill the time available, that housing demand will expand as more houses are built. As long as the population keeps growing, we will never have "enough" of whatever type of housing is currently in demand. (This is even before we consider the environmental impact of increasing urban sprawl and the morality of encouraging it).