he logic seems obvious. This country has too little space for housing, too much for retail, so why not convert the latter into the former? As the effects of the pandemic scythe through high street brands – Café Rouge, TM Lewin, Carluccio’s, Bella Italia – felling what were in many cases already wilting businesses, it makes sense, on paper, to hand over the spaces they vacate to people desperate for somewhere to live. Let us therefore take the step, unusual in these pages, of agreeing with the prime minister. Shortly after he announced his “new deal” last week, he proposed that shops “be converted into residential housing more easily”. There would be the added benefit that any homes achieved in this way would, in theory, reduce the pressure on the nation’s green belts. They might also help to revive towns whose economic and social energy was flagging. High streets will change and are changing in any case. Some things familiar and some loved will be lost. But it would hardly be a bad thing if more people lived in the centre of towns, with a 24-hour concern for the places near their home, and some money to spend on such local retail – hopefully, the more independent kind – as remains. It might make British towns more closely resemble admired continental examples, where homes and businesses more intimately co-exist. The loss of jobs in retail and restaurant chains is devastating for those involved, but their tendency to homogenise towns is not something to be mourned. Much retail consists of malls, both out-of-town and in town centres, often land-hungry developments with huge car parks. It would not be a loss to the nation’s urban fabric if some of these became housing. In the great sweep of history, the high street as we know it is not an eternal feature but largely an 18th- and 19th-century creation, replacing economies more dependent on both markets and individual households’ growing of produce for their own use. If town centres changed before, they can do so again. The devil, though, is in the detail, a territory that Boris Johnson finds notoriously hard to navigate. “You’ve taken me into a sort of rabbit hole of detail,” he bemoaned, only last Friday, to LBC’s Johnson-friendly interviewer Nick Ferrari. And to change a shop into a home, or a mall into apartment blocks, is not something to be done with a snap of the fingers. They tend to be different shapes, with significantly different requirements for such things as daylight, privacy, views and open space. There’s not much reason to think the government knows how to address these questions. The main tool in its box seems to be the relaxation of planning rules, so that property owners and developers can switch uses from shop to home without the usual processes of application and permission. This is something it has already tried, by extending what are called permitted development rights (PDR), such that offices can be made into flats. The results have been atrocious, leading to the creation of entire flats no bigger than standard double bedrooms, often with no cross-ventilation and no outdoor space. The waiving of planning rules has produced horrors such as Terminus House in Harlow, Essex, a 14-storey “human warehouse” where London boroughs have been offloading people from their housing waiting lists. Here, families are crammed into studio flats, and drug gangs fight turf wars in corridors and lift lobbies. The main entrance to the block is through the bin store. Some homes have been proposed without windows, which the government will now stop, but it is hardly a mark of a civilised country that such a thing should even have been a possibility. The conditions created by PDR would be intolerable in any circumstances, but Covid-19 has demonstrated more than ever the importance of adequate personal space. It is easy to see how a similar approach would play out with shops – imagine what would happen if developers converted a butcher’s meat store into a home as cheaply as possible, or tried to make an old supermarket into as many residential units as possible. Some wit also needs to be applied to the collective as well as the individual implications: the loss of shops in the wrong place will accelerate the decline of high streets’ economy, not arrest it. Perfectly healthy retail businesses will be closed down, simply because a landlord can make more money by divvying up the premises into flats. As for the larger scale, the government would be naive to think that an end to what Johnson called the “newt-counting delays” of the British planning system will alone cause developers to build thousands of beautiful homes on shopping malls. British housebuilders do not, have not and will not build homes of the numbers required, because it is not in their interests to do so. They are even less likely to create the affordable homes that millions need. It is a laissez-faire fantasy to think that commercial animal spirits, unbound by red tape, will achieve everything by themselves. In announcing his undernourished new deal, Johnson noted that Germany and the Netherlands have higher rates of homebuilding than in Britain. What he failed to say was that those countries’ governments are considerably more proactive than ours, both in building social housing and acquiring land, and making the investments in planning, infrastructure and remediation that enable development to happen. The state, in other words, has to get involved. As mayor of London, Johnson’s bright idea for increasing housing numbers was to make it easier for developers to build bigger and taller blocks of expensive units, much of it sold as investments rather than homes, most of it of little relevance to the city’s needs. The signs now are that he is planning another giveaway of development rights, one that will enrich landowners without achieving the transformation of housing that he promises. His proposed changes to high streets looks reasonable in theory but catastrophic in practice. •Rowan Moore is the Observer’s architecture critic