With Labour struggling desperately in the polls, local initiatives are emerging to try and provide a united left-of-centre challenge to the Conservatives in key seats.

The local Green party has announced it will not run against Rupa Huq, the Labour MP for ultra-marginal Ealing Central and Acton, while Women's Equality Party leader Sophie Walker is seeking a united front against controversial Tory Philip Davies in Shipley.

Meanwhile campaign group Compass is bringing together activists from different parties to try and create some form of "progressive alliance" to stave off the Conservative tide at local level.

The idea of all these initiatives is that it's easier to put Labour's fractured electoral coalition back together through informal co-operation and non-competition rather than aiming for formalised unity at party level. Which is true. And that by doing so, it might be possible to stave off Brexit - or at least hard Brexit - plus austerity measures and benefit cuts. Which is not true.

My team's bigger than your team

It is tempting to look at the Conservative margin of victory in the seats that secured it an overall majority two years ago, see the votes won by third-placed and fourth-placed parties, and assume that if they all got together the Tories could have been kept out.

But there are also signs that Ukip is allowing eurosceptic Tory MPs a free run this time round - and in any case, the Ukip vote is collapsing and flowing to the pro-Brexit Conservative party. That far exceeds the impact of the Greens in most seats.

Not all Liberal Democrats are left of centre. Not all Ukippers will vote Conservative - or at all. Party loyalty overrides most tactical initiatives. But if we take English seats - Scotland's battle lines are different, while the politics of Plaid in Wales are complicated - and combine the Labour, Lib Dem and Green votes in each seat from 2015 on one side, and Tory and Ukip votes on the other, then the Tories in fact do better than before.

In 2015, the Conservatives won 330 seats across Great Britain. But if the vote had been between two "alliances", the right-wing side would have won 349 in England alone - including sizeable majorities in once-safe Labour turf such as Walsall North, Dagenham and Rainham, and Wakefield.

Bishop Auckland, Bradford South and Penistone and Stockbridge would have tipped over the edge to the Tories, as large Ukip votes took effect. The Labour-led alliance would have held Workington - won by Labour at every general election for nearly a century - by five votes.

Add in the 11 seats won by the Conservatives in Wales, and the right would have taken 360 seats - an overall majority of 70, bigger than Blair's victory in 2005.

But that was 2015. There is little that has not changed since then. The Conservatives are anywhere between ten and 25 points ahead in the polls. The Lib Dems are recovering in some seats, but making slow progress in national polls. The Greens are marginal. Labour is in meltdown.

As Chris Hanretty explained last week, the British Election Study shows that Labour support is weakening and Conservative support strengthening in Labour's own seats relative to other seats - in other words, the Tories are disproportionately gaining ground, and Labour losing ground, where it hurts Labour most. They are outperforming the polls in the marginals. Labour majorities of 14% would be at risk.

What's worse, Hanretty used data from November and December 2010, when the most recent BES research took place. The Tories' poll lead is stronger now than it was then. Labour seats with 20% majorities start coming into play. That takes in Sedgefield, by the way - a large but soft Ukip vote means even Tony Blair's old seat cannot be taken for granted by Labour.

What all this means is that the Conservatives, sweeping up Ukip votes and resurgent in Scotland and Wales, are looking nailed on for a majority of at least 100 - possibly much, much more.

Too little, too late

A progressive alliance, in those circumstances, can do little more than scoop buckets of water from the deck of the sinking Titanic. Nor could an alliance have been put together once Labour decided to support Brexit - the Lib Dems are seeking to win votes from both Labour and the Tories, while many left-wing Labourites have not forgiven Farron's party for the coalition. A specifically anti-Brexit alliance would risk further seepage of Leave votes to the Tories - and well off Tory Remain-voters in the Home Counties are just as likely to stick with "strong and stable" Theresa May as they are to switch to Tim Farron.

A progressive alliance may have a small impact in certain seats, mostly in London, perhaps most effectively not even against a Tory MP but Labour Leaver Kate Hoey. Had an alliance been hammered out earlier, taking in the Liberal Democrats, committing to the single market, and encompassing more seats, it would have given May cause for concern - it probably would have discouraged her from calling a snap election.

Instead, it risks becoming another footnote in the shattering of the 1997 coalition of voters that took Labour to power - no longer seeking power, but merely hoping to recreate Ed Miliband's inadequate vote of 2015.

That would be a huge achievement in the circumstances. It won't happen. The Conservatives are heading for a very large majority, with which they'll be able to do as they please - on Brexit strategy, on benefits, on bus services, on everything. The trouble with a progressive alliance is there aren't enough progressives to go round.

Chaminda Jayanetti is a freelance journalist. You can follow him on Twitter here.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners