One night in 1967, Ronnie Hughes, then a 12-year-old boy who lived with his family on a new estate at the edge of Liverpool, was allowed to stay up late to watch Cathy Come Home, Ken Loach’s TV film about homelessness in modern Britain.

Watching it changed Ronnie’s life, as it did many others who were shocked into action. On leaving school, he became a housing officer and has worked to provide good housing for people who need it ever since. Now, through the social enterprise Coming Home, he brings empty homes in Liverpool back into use for secure tenancies at low rents.

The housing charity Shelter was also set up because of Cathy Come Home and the film’s impact was such that its title and its theme – if not its lessons – have never been forgotten. So why, 50 years after it was first broadcast, is Britain facing a homelessness crisis on the same scale?

I could sum it up in one word – Tories – and that wouldn’t be egregiously inaccurate. As a teenager in 1990, I visited London for the first time and saw the “cardboard city” at Waterloo, scarcely able to believe what I was seeing, but perfectly aware that it was there because of the government of the time. Around that time, seeing people sleeping and begging on the streets was a sad and anger-making part of living in a big city.

Once Labour entered power in 1997, visible homelessness pretty much disappeared within a few years. Tories, again, would try and pin that on the “green shoots” of economic growth, but street homelessness was ended, if temporarily, by sustained and specific government funding for the organisations and individuals who knew what needed to be done.

Now homelessness is back in all its forms. Everywhere you go, people are back living on the streets, desperate and dishevelled. One man in the subway beneath Birmingham’s Rotunda sits with a sign saying: “I am a homeless person but I feel INVISIBLE!” There are small tent cities in Manchester and those terrible, familiar cardboard-box beds in doorways.

It is no coincidence that this phenomenon has returned in the last seven years – more intensely in the last two, since the Tories managed to shed the Lib Dems – although the wider housing crisis has been decades long in the making. The widespread housing insecurity now experienced by millions was avertable and reversible at any point, but for lack of political will and public outrage.

Throughout the 1960s, demographers based population forecasts on the birth rate during the postwar baby boom, predicting that the population of Britain would pass 70m before the end of the 20th century. Housebuilding and slum clearance were already close to the top of the political agenda when Cathy Come Home was broadcast, with the completion of new homes, mainly council houses and flats, based on those population projections, reaching 350,000 per year by the late 1960s.

By the mid-1970s, there was, technically speaking, a surplus of housing in the UK, with council estates housing a third of all households. The Tories couldn’t be doing with a situation in which, in crude terms, most people’s basic needs were met without significant personal sacrifice. In 1980, they introduced the “right to buy” council homes, so that “deserving” working-class people could saddle themselves with a mortgage and, over time, what was left could be fought for by the “undeserving”.

As long ago as 1993, researchers at the Joseph Rowntree Foundation, in a report tellingly titled Making It Happen: Finding the Resources for Social Housing, noted that 600,000 more homes would have been built in Britain during the 1980s had we invested the same proportion of GDP in housebuilding as West Germany did during the same period.

The Commission on Social Justice, set up by Labour leader John Smith before his untimely death in 1994, commented in its final report that “for the large number of homeless people, housing is an aspiration rather than a reality”, and recommended: “If we want to end the scandal of homelessness in all its forms, we need to build and refurbish more homes for rent at affordable rates.”

Just why do we need to repeat this demand in 2017? We know that the calls of the commission weren’t really fulfilled by the Labour government, which took the report’s more third way elements on “rights and responsibilities” and the market “having an active role to play” to more pronounced ends than a government led by Smith may have done.

During Labour’s time in power, a sustained slump in housebuilding occurred. When, in 2007, Gordon Brown announced a programme to build “200,000 new homes a year”, it sounded radical and has sounded radical every time a prime minister or party leader has announced the same target since then. In that time, the shortage of secure and affordable housing has spread far beyond London and the south-east to include most towns and cities.

So what is to be done? For one thing, work to bring about a change in government as quickly as possible. The existence of extensive and long-term homelessness is ideological. Academics David Whyte and Vickie Cooper describe austerity as being a calculated programme of state violence against the most vulnerable and I don’t disagree with that.

The Tories cling to power because they manage to persuade just enough people at any one time that living in shop doorways, hostels or B&Bs is an individual lesson in character-building. They cannot afford to remind the public that people only do it because they do not have a home of their own to sleep in at night. Get rid of them, then encourage a Labour government to build more, build well and encourage community groups to build. (This is already happening in Leeds and Liverpool.)

It is bloody expensive to treat people as badly as this government does. The royal borough of Kensington and Chelsea has enough cash in reserve to buy dwellings within its own borough to permanently rehouse everyone made homeless by the fire at Grenfell Tower, but instead it obfuscates the clear need for swift justice and puts up survivors in hotels, where they can’t settle.

Street homelessness could be ended within a year and other forms of homelessness caused by eviction, penury and structural disadvantage eradicated in a single term of government if it was made a political priority over Brexit, Trident renewal or any other needless diversion. Cathy Come Home demanded that we change the way we see “home”: to regard it as a right, not a reward. It’s time to make that demand again.