What a difference a week makes. Last week, the Institute for Fiscal Studies made many of the front pages with a partisan and breezy dismissal of Labour’s plans as “simply not credible”. Today, in its analysis of the three major parties’ manifestos, it conceded that Labour’s “vision is of a state not so dissimilar to those seen in many other successful western European economies”. Public spending would be at a lower share of national income than Germany and many other European countries.

The headline reporting – that neither Labour nor Conservative spending plans stand up to scrutiny – occludes the IFS’s more important message: that Britain faces a fundamental choice about its future direction. The organisation’s director, Paul Johnson, noted that the Tories were offering “more of the same” and that “there is little to say about Conservative proposals” since “they believe most aspects of public policy are just fine as they are”. In contrast, Johnson argued that Labour has “vast ambition” and that it wants to “change everything” – but questioned whether this was achievable.

IFS analysis reveals the dishonesty of the Conservatives’ stated plans

The Tories appear to have broken with the political consensus formed after the Brexit referendum: that the public are hungry for change. Their commitment to the status quo is both an enormous political gamble and a rebuke to working people whose wages have been stagnant for a decade, to the sick waiting for NHS treatment, the elderly suffering from a social care crisis, and more than 4 million children living in poverty. It is hard to view it as anything but a monument to born-to-rule entitlement: victory is assumed rather than earned. In the face of a social and economic crisis, the Tories will face the electorate with a solemn promise to do nothing.

Yet the emptiness of the Conservative manifesto should come as no surprise: it is the logical conclusion of a lost decade for Britain. For nearly 10 years now, Conservative thinking has been defined by the presence of absence: an ideological programme of austerity to slash back the state. The IFS confirmed today that austerity was now “baked in” to Tory plans for the future. Where an active state should be, the Tories intend to leave a void.

As a political project, Brexit merely prolongs the void, with a false promise that all the problems of the present will magically be solved. In truth, there is no substantive problem to which Brexit is the solution; instead, it nourishes and sustains the nothingness. The IFS starkly warned that Johnson’s “die in a ditch” promise to terminate the transition period by the end of 2020 risked doing serious economic damage.

The impulse to destroy rather than to create has become the hallmark of 40 years of Tory government – wrecking our industrial base and trade unions under Margaret Thatcher, the public realm under David Cameron, and our international relationships under Theresa May and Boris Johnson.

But perhaps the most revealing aspect of the IFS analysis was the dishonesty of the Conservatives’ stated plans. The IFS points out that the Tories “would end up spending more than their manifesto implies and thus taxing or borrowing more”, with their proposals riddled with uncosted commitments and vague aspirations. Perhaps it should be little surprise that the character of the Tory manifesto reflects the man who leads their party.

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In sharp contrast, the IFS criticised Labour’s planned increases to public investment, arguing that the public sector lacks the capacity to “ramp up that much, that fast”. But more importantly, it appears to have accepted the central argument Labour makes: that increasing spending and investment has a multiplier effect that would boost economic growth. In a surprise conclusion, it found that Labour’s plans could boost output by £22bn, returning about half that in tax – vastly more than the £5bn assumed by Labour’s own plans.

That’s because the fundamental problem in the UK economy is chronic under-investment. For 40 years, public and private investment have trailed behind other advanced economies. The result? According to the Bank of England, nine-tenths of economic growth comes from consumption rather than investment, made possible by unsustainable levels of private debt. Labour’s plan would boost public investment to Scandinavian levels to catch up on the backlog, and to stimulate investment from the private sector.

The IFS analysis concludes that Labour’s manifesto should be seen as “a long-term prospectus for change rather than a realistic deliverable plan for a five-year parliament”. And in this lies a deeper truth. People and governments commonly overestimate what can be done in two years, but underestimate what can be achieved in 10. Under a Labour government, Britain would be a radically different country at the end of the 2020s than at the beginning.

In an era of unprecedented demographic and technological change, surely the biggest threat to Britain’s future is to attempt to keep things the same and muddle through, which is all that the Tories now offer. The truth is that fundamental change is now needed to enable the economy to achieve escape velocity from the void in which it has been trapped for a decade. As the IFS said today, the choice could not be starker.

• Tom Kibasi is a writer and researcher on politics and economics. He is writing in a personal capacity