In today’s troubled Britain, it is commonplace to say that the political parties need to come up with some fresh ideas to transform the country. But what happens if one of the big parties starts announcing radical new policies and yet most people don’t seem to be listening?

That sobering question hangs over Labour’s hugely ambitious but so far only moderately successful election campaign, judging by the slow improvement in its poll ratings.

Yet the answer could be less bleak for the party, and for the country, than you think. Whether Labour loses or wins, in this campaign it has begun to set out a new, potent notion about how politics should be done and what elected politicians can achieve.

It's making promises of a scale and novelty rarely encountered in the often content-free world of British electioneering

The party hasn’t even published its manifesto yet. But already it’s making promises, on an almost daily basis, of a scale and novelty rarely encountered in the cautious, often content-free world of British electioneering.

At Labour events in Liverpool, Manchester and London in the past fortnight, I’ve heard the shadow chancellor, John McDonnell, promise “an irreversible shift in the balance of power and wealth in favour of working people”; the shadow business secretary, Rebecca Long-Bailey, promise “a new era of public luxury for all our communities”; and the shadow health secretary, Jonathan Ashworth, promise that “The NHS will literally be rebuilt under a Labour government”. “I want our children,” he went on, “to become the healthiest in the world!”

On each occasion, the reaction from party members in the audience was enthusiastic but not ecstatic. Since Jeremy Corbyn became leader, four febrile years ago, they’ve got used to the party unveiling ever more radical blueprints for government, not always with precise timetables and costings attached.

Yet for anyone whose sense of the party was formed during the 30 years before Corbyn took over, Labour’s current boldness can still feel pretty startling. During Tony Blair’s long leadership, I sat through countless New Labour election launches, always beautifully choreographed, at which Blair or one of his lieutenants would energetically announce the party’s intention not to upset the status quo very much. As he wrote in their 1997 election manifesto, “I want to renew our country’s faith in the ability of its government … by making a limited set of important promises and achieving them.”

Play Video 1:52 Jeremy Corbyn promises free broadband under Labour – video

In that crushingly effective New Labour campaign, the party’s main promises were sparse and modest enough to fit on a pledge card the size of a credit card. And two of the five – “no rise in income taxes” and “fast-track punishment for persistent young offenders” – were the same in spirit as policies the Conservative government had been pursuing for the previous 18 years. New Labour was expansive in its marketing and electioneering. But in another, crucial area – how bold the policies of left-of-centre parties could be – it offered only a drastic and dispiriting contraction of the political.

Corbyn’s party has done precisely the opposite. The shape of the economy, the distribution of wealth, the future of work, the role of the state, the purpose of foreign policy – all these and other awkward questions have been thrown into the everyday political debate. The establishment has responded with a mixture of bafflement, fury and anxiety. All those were immediately on show this week after Labour’s surprise announcement that it would nationalise and modernise Britain’s rickety broadband network. From crude Tory tabloids to suave centrist lobby groups, the same basic desire is visible: to destroy or neuter Corbynism as fast as possible, so politics can be narrow again.

These enemies of Labour radicalism have grounds for hope. Twice before in its modern history, the party has gone into an election vainly promising radical change. In February 1974, under Harold Wilson, Labour won narrowly with a manifesto promising “a fundamental and irreversible shift in the balance of power and wealth in favour of working people and their families” – McDonnell’s current borrowing of most of this phrase is not a coincidence. But the wily centrist Wilson went on to govern in a much less adventurous fashion. Nine years later, in 1983, another iconoclastic Labour manifesto proposed controls on the City of London and unilateral nuclear disarmament. It was widely blamed for Michael Foot’s heavy defeat.

Yet the conditions for leftwing radicalism are more favourable now. In 1974 and 1983, Britain was moving to the right in its underlying political and social attitudes. These days even Tories rarely make that claim – not after the financial crisis, the discrediting of austerity and the dawning realisation that free-market capitalism, at least in its present form, is not compatible with saving the planet.

The growing recognition of the climate emergency has begun to shift our sense of what it is possible – or necessary – for governments to do. Labour’s proposed “green industrial revolution”, which would see government and business collaborating to produce new green technologies, may turn out to be an ingenious way of creating better jobs and improving economic growth. But it could also be a clever way to attract the votes of both environmentally conscious millennials and middle-aged factory workers.

Play Video 1:55 Javid v McDonnell: Tory and Labour parties reveal economic plans – video

In Labour literature and speeches generally, it’s striking how often the climate crisis is invoked. Since how we all live is going to have to change fundamentally, the underlying argument goes, why not vote for the only big party in Britain – and, arguably, in Europe – that believes in fundamental change? Labour’s engagement with green issues, belated but deeper than before, has given the party a new confidence.

Even Brexit, while quite possibly disastrous for Labour now – the toxic, nationalist glue holding a flimsy Tory government together for another term – may contain a more hopeful message for the long term. Leave’s stubbornly persistent support shows many voters are still in a disruptive mood, ready to support risky schemes to change the country, regardless of the establishment’s warnings. That mood helped Labour at the 2017 election, and may help it again.

The problem for the party, now and in the future, is how to sell radicalism to voters, and journalists, who have not considered a radical plan for government since Margaret Thatcher’s in the 70s and 80s, and may have forgotten how to do so, or even how to make the effort. Working out whether you think state-run broadband is a good idea takes a bit of time. It’s much quicker to decide you just don’t like Corbyn.

Already, many centrist commentators concede that his party has a lot of good ideas, and some of them are beginning to endorse the idea of “Corbynism without Corbyn”. That’s how far British politics has quietly drifted to the left since 2015. Tory election win or not, that drift may be hard to stop.

• Andy Beckett is a Guardian columnist and author of Promised You a Miracle: Why 1980-82 Made Modern Britain