Next month the Conservatives will have been in power for 10 years. British parties who manage that anniversary are usually unpopular by the time it comes.

In 1989, Margaret Thatcher’s government lost its poll lead for good. By 2007 Tony Blair was no longer a dominant premier. Accumulating mistakes, personal burn-out, the difficulty of finding fresh goals and voters’ boredom with the status quo; all usually ensure that even parties with able leaders weaken and fall from power after three or four terms. To a large extent, the UK’s traditional sense of itself as a diverse, healthy democracy depends on it.

Yet recently our revered political pendulum seems to have stopped swinging. Last year, the Tories won their fourth consecutive general election, by a far larger margin than the others. Since then, their poll lead has swollen further. They are widely expected to win a fifth election, whenever it comes. No British party has done that since the early 1800s.

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This Tory ascendancy has been maintained despite a record in office since 2010 that is arguably worse than those of the UK’s most infamous modern governments, the overwhelmed Conservative and Labour administrations of the 1970s. The Tories have called and lost the EU referendum, pushed Scotland and Northern Ireland towards leaving the UK, pursued austerity policies that hugely damaged public services and society – without reducing government debt as promised – and presided over the worst wage growth for two centuries. Now they appear to be mishandling coronavirus catastrophically. Labour has never been allowed to forget its smaller failure to halt the winter of discontent, more than 40 years ago, when strikes notoriously delayed the burial of some people who had died of natural causes. After coronavirus, Britain may associate the Conservatives with far worse horrors.

But that is not happening yet. Surveys show some mild public disapproval of their performance during the crisis. Yet there remains a general acceptance that, for the foreseeable future, for good or ill, the Tories will be our masters. Such feelings can be self-fulfilling. In 1954, the French sociologist Maurice Duverger wrote: “A dominant party is that which public opinion believes to be dominant.”

And Boris Johnson’s administration seems to be seeking a more complete dominance than previous British governments. It demands compliance rather than frankness from Whitehall. It excludes critical journalists from official briefings. It avoids scrutiny by parliament: the Commons has sat for one full month in Johnson’s first 10 as premier. Meanwhile, the Tories have repeatedly claimed to represent “the people”, as if no other party can.

In all these ways, the UK may be moving closer to becoming a one-party state. Not a totalitarian one, but a democratic one, like postwar Italy or Japan, where one party is in power for decades, on its own or in coalitions, absorbing ideas and policies from rival parties, shamelessly moving rightwards or leftwards according to circumstances, and winning the pragmatic support of ever more interest groups. The life of a single party – its ideological trajectory, factional struggles and leadership contests – becomes almost the whole of politics.

For some voters, one-party democracy is a relief. It saves them having to think much about politics, from having to evaluate other parties. Last year’s Tory victory owed a lot to this impulse: voting in a third general election in four years, some people were tired of having to consider Labour’s alternatives, and settled for what they knew.

In the UK, one-party democracy does exist in non-Tory forms – thanks to devolution policies enacted by Labour. Wales has been continuously governed by Labour (sometimes in coalitions) since 1999, Scotland by the SNP since 2007. And concerns about the UK’s tendency to produce democratic monocultures pre-date the present Tory era. Twenty years ago, under Blair, the political scientist Colin Crouch coined the phrase “post-democracy” to describe the contraction of electoral politics to “a small range of issues”, selected “by rival teams of professionals”, while more fundamental questions were settled in private by big business and deferential politicians.

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In one sense, our democracy is healthier now. Labour and the Tories disagree much more profoundly than they did during the Blair years – voters have a proper choice. But in other ways, what we have now is worse: a political system dominated not by “professionals” – New Labour’s bland but often competent and hard-working ministers – but by amateurish Tory figures.

Will this one-party democracy last? Parliament finally returns next week. The government’s clear failures over coronavirus continue. Labour has a prosecutor for a new leader. And the Tories, for all their electoral supremacy, still look ill-equipped to deal with the crises that will return to prominence after coronavirus: over the climate, the viability of modern capitalism, and how to create a society that works for all age groups, rather than mainly the old and middle-aged. These questions are likely to be too divisive to be settled inside one party.

When the Conservative era eventually ends, it may do so spectacularly. As many dictators and long-serving premiers have discovered, there’s one big problem for practitioners of one-party rule. When the public finally decide that you’ve failed to deliver, there’s no one else to blame.

• Andy Beckett is a Guardian columnist