The British electoral system is both cruel and crude. In a winner-takes-all, first-past-the-post setup, many votes are wasted, the main parties are overrepresented in the House of Commons and if people want to make a difference, they often have to ignore their first preference and vote tactically for their second. It’s a third-rate system, but it’s the one we have.

Twenty two years ago, when I edited the Observer, we published polls in 20 key constituencies on the Sunday before the 1997 general election, urging voters to put aside their first preference and vote tactically for the most likely challenger to the incumbent Conservative party. Our work did make a difference, triggering the Michael Portillo moment, for example, when one of the leading Eurosceptics lost his ultra-safe seat as Lib Dem voters set aside their first preference because of the evidence that Labour was the challenger.

Today, the stakes are much higher. Again, the Observer is publishing a guide, compiled by the eminent pollster Peter Kellner, to which party lies second, this time in 50 seats; without tactical voting to create more Portillo moments, Britain will face another five years of Conservative government. We need tactical voting to have as great an impact on Thursday.

Today’s Tory party is not that of John Major or even David Cameron. To destroy Nigel Farage’s Brexit party, it has cynically and ruthlessly killed off its liberal wing. It has made a Faustian pact with a leader it knows to be callow and untrustworthy; Boris Johnson is Britain’s version of Trump or Berlusconi. This Brexit party in all but name has deployed the Tory brand and widespread contempt for Jeremy Corbyn to consolidate the Leave vote while the Remain vote fractures. It has every prospect of winning a comfortable working majority – maybe to win big.

In which case, relative economic decline and social distress are guaranteed to intensify while the bonds between governors and governed will become ever more toxically distrustful. Abroad, the country will become a leper on its own continent as it ruptures the benign trading, security and co-operative relationships built up with our neighbours over 46 years of EU membership, a rupture justified by lies, evasions and half-truths on an industrial scale that have so tragically polluted our public life. To oppose this, we only have days to marshal tactical voting power.

The Labour party has suffered predictable derision for its economic plans and it made a strategic mistake in promising so much, so fast and so expensively through a new network of untried, top-down statist institutions, justifying some of the derision. But at least it is an attempted solution to Britain’s problems of low growth, poor productivity and profound spatial, income and wealth inequalities – and it steps up to meet the climate crisis and environmental challenge head-on. Above all, Labour offers to reshape Brexit so there is a second referendum choice between a minimally economically damaging exit or none at all. There could be a way out of the conundrum that offers national resolution in a less self-destructive way.

Hopes that a US trade deal will offset the damage are moonshine

Instead, Johnson’s Tory party promises to complete the rightwing coup that Brexit constitutes, along with deepening economic, social and cultural division. Johnson wants the break complete by the end of next year, an impossible timetable. But with a parliamentary majority, he can push through a no deal if it is not met.

The best that could be hoped for if we leave the safe harbour of the EU’s economic area is years of little economic growth as our businesses reel from broken supply chains, time-consuming customs checks, choked-off inward investment and only expensive access to our closest markets in Europe. Meanwhile, world markets become a wild west of growing trade protection as WTO rules collapse in the wake of the closure of its appellate court last week. At worst, there will be an economic slump that will threaten the viability of our already rickety financial system.

Hopes that a US trade deal will offset the damage are moonshine. Apart from how long it will take to negotiate, it involves necessarily working with a uniquely predatory capitalism along with its industrialised, inhuman agricultural sector – some steps away from the values Britain holds dear. The Tory manifesto is conspicuous for not going near any reset of capitalism so that it works more for social benefit; nor is there an industrial strategy. Britain is to trust in the magic of US-style rapacious business and cripplingly unfair labour markets, alleviated by the magic wand of infrastructure spending.

This can only deliver low and unbalanced growth. Life expectancy is declining in the Brexit-voting parts of the north-west, north-east, Yorkshire, Humberside and East and West Midlands. As deindustrialisation accelerates with Brexit and without any agency to bring back economic life, the relative decline of these regions will accelerate, as will the fall-away in life expectancy. No determined effort to alleviate soul-destroying poverty, especially for an estimated 4.5 million children, or to radically enhance skills and life chances is planned by the Tories. Instead, expect more of the same against the darkening background of Brexit.

Yet the tribe will cement its hold on the state. Already, the prior qualification for any public appointment – from the chair of NHS England to a trusteeship of the British Museum – is to have lent active support to the Tory party. It now wants to extend its grip to the upper echelons of the civil service and judiciary.

Pressures will grow in Scotland and Northern Ireland to leave the union. Public service broadcasting will be diminished, with the BBC forced to retrench as it unfairly funds free TV licences for the over-75s. The attack dogs of the rightwing press will be offered ongoing permission to act as surrogates of government newspapers. Civic and political life will become a democratic charade.

Only a hung parliament can save Britain from this fate. Labour, whatever it may say now, with fewer votes in the House of Commons than the Conservatives, will only be able to pass the most feasible and least contentious elements of its programme – but will deliver the vital second referendum on EU membership.

The Tories may have made their Faustian pact with Johnson. There is no need for the country to do so too. Vote tactically this Thursday.

• Will Hutton is an Observer columnist