Labour has held the Cumbrian parliamentary seat of Copeland continuously for more than 80 years. Yet the Conservatives are odds-on with the bookies to win the byelection that is due there in early 2017 following Jamie Reed’s resignation. The odds reflect a wider scepticism at Westminster about Labour, as well as a feeling that a Tory win may bring on an early general election.

There are, though, good reasons to be doubtful about almost every aspect of this. True, the Labour majority in Copeland in 2015 of less than 3,000 looks vulnerable at a time when the national polls give the Tories double-digit leads and the Labour national share is as low as 25%.

Yet Labour has a decent record of holding its seats in byelections since 2015. And Copeland, like west Cumbria as a whole, is very much its own place.

Providing it chooses a candidate in the Reed template – which means a pro-nuclear local candidate backed by the GMB union – and also that it fights the contest hard, then a seat dominated by the Sellafield plant may prove a tough nut for the Tories to crack. Copeland may be made of more dogged Labour stuff than London-based pundits who have never been to Cleator Moor or Egremont may assume. Providing Ukip does not withdraw to give the Tories a clear run, my money would still be on Labour at this stage.

But Copeland and other recent byelections have rekindled a wider debate about UK party politics and election strategies. The matter in question is whether the parties of the left of centre, loosely defined, should be more open to electoral and political cooperation of various kinds in order to prevent the Tories re-establishing a rightwing English-based post-Brexit hegemony over British politics for the foreseeable future.

For the reasons just stated, Copeland may not be a particularly good test bed for this “progressive alliance” thinking. Although the Liberal Democrats and the Greens ran candidates against Reed in 2010 and 2015, their voters are likely to be anti-nuclear. So there is little prospect of them backing a Labour candidate whose central pitch is likely to be the defence of Sellafield and the thousands of relatively well-paid jobs it generates. For the same reason, Labour has no incentive to court these voters.

‘Copeland, a seat dominated by the Sellafield plant, may prove a tough nut for the Tories to crack.’ Photograph: Owen Humphreys/PA

Nevertheless, the progressive alliance option is undoubtedly a growing debate. At its core are three propositions. The first is that the majority of people in the UK do not vote Conservative, so the non-Tory parties need to cooperate more. The second is that Labour’s historic late 20th-century dominance over the UK’s non-Tory party politics is in decline, so these forces need to cooperate if they are not to be endlessly eclipsed by the Tories. The third is that Britain needs a new 21st-century, post-industrial progressive agenda that takes more account of factors including inequality, localism and climate change.

No one who writes professionally for the Guardian can dismiss any part of this. More than 100 years ago, this paper’s owner and editor CP Scott often wrote in favour of cooperation between the Liberals and the newly emerging Labour party, warning that failure to do so would mean “the Conservative dog running away with the bone”. The Guardian has editorially been broadly in favour of devolution, electoral reform and political alliances for most of the last century – and last time I looked it still was.

Yet no one who tries to think objectively about modern politics can close their mind to the many problems. One of the most heretical for some readers is that supporting or opposing the Tories may not in fact be the defining divide of British politics. Those who define themselves on the left need to be open to the thought that Labour may in fact provide an equally important divide. There are also, whisper it who dares, progressive Tories as well as reactionary ones. It ought not to be a thought crime to consider that Ruth Davidson or David Willetts are more sympathetic political figures than some in the Labour party.

A second problem is that the left is in a political pickle in many developed countries today precisely because it doesn’t have the answers to today’s problems, not because the political systems make it difficult to get its apparently virtuous answers across. The problems themselves are fairly easily stated: climate change, obesity, over-mighty financial services, declining real wages, widening inequality, ageing population, democratic failings. The answers are much harder. No party has them.

A third and crucial problem is that active cooperation between parties eventually has to come down to nuts and bolts. Here the going gets tougher. If it involves electoral pacts, how extensive should they be? What is the policy towards the Scottish and Welsh nationalists – are they part of the alliance too? Supposing that an anti-Tory alliance won a general election: who would get to be in government, and are all MPs from the different tribes bound to support that government on all major votes?

We are getting ahead of ourselves here. But it is important to know where the progressive alliance proposal is intended to lead. Even at this embryonic stage, when an alliance is still mainly an idea not a reality, the truth is that the two major potential cooperators, Labour and the Liberal Democrats, more frequently despise one another. Nothing would make them cooperate in the southern Tory seat where I live, for instance, even though the sitting MP is eminently beatable if it happened. Nor can it be taken for granted, as Copeland reminds us, that everyone who wants the Tories out shares the Greens’ hostility to nuclear power or cars.

Making alliances is difficult. It means being pragmatic and tolerant. Many on the left are neither. In the end, with the massive exception of Brexit, the great unknown in British politics in 2017 is still whether the Labour party has a viable future as a party of government, not what comes afterwards.