> Perhaps you've heard of the problem of "vote splitting"
What vote do you think is being split? Some kind of generic not-Conservative vote? People vote for other parties - they aren't split among a vote not for the Conservatives.
If it really were simple vote splitting then coalitions would form, and they don't - because the other parties aren't a simple platform of not-Conservative and they disagree with each other as much as they disagree with the Conservatives. In fact one of the only two parties to successfully coalesce was the Conservatives!
As a concrete example - the second choice in most parts of Scotland isn't Labour, it's Conservative. Are the Conservatives and Labour splitting the not-SNP vote? If you think that then is any party that stands except the ruling party a vote splitter? Seems a silly definition to me.
> Well, try 51% for a start.
An absolute popular majority? I don't think that's realistic and it would be extremely unhealthy if that was the case.
Look, you obviously haven't sat down and actually read about this as you are clearly not aware that yes, every single election the combined 'left' vote, Labour, SNP, Green, Plaid Cymru, etc. is over 50%.
The left would clearly win the last election, but because of FPP and gerrymandering in the UK, that's been going on for decades, they don't.
It's one of the reasons they don't sort the house of lords, as the likely solution would be representative which would basically permanently end the Conservatives being elected for anything.
I've voted Red, Blue and Yellow over the years, so this isn't bias, I'm just tired of the latest batch of blue as they are utterly incompetent and part of the reason is the present, completely stacked, British electoral system.
If they could do this they'd form a coalition and form a government, but they don't.
Why do you think that is?
Because they don't really share many ideals, principles, or policies. You can look at them and call many of them 'left', but other than that they're not really compatible. Some are nationalist, some are unionist, some are progressive, some are regressive (often within the same party!) What do you think they have in common? What direction would they work?
For example are the Liberal Democrats part of your left block that would win? But when given the choice they coalesce more readily with the Conservatives in practice.
I'm not the commenter above, but I appreciate your polite and good-faith discussion of this issue, so I hope you don't mind me presenting the counter-argument in their absence.
> If they could do this they'd form a coalition and form a government, but they don't.
In order to form a coalition, parties need to collectively have enough elected MPs to hold a majority in the House of Commons. A major point we are making is that the electoral system in the UK allows the Conservatives to gain a disproportionate number of seats, unreasonably preventing the other parties from being in a position to form such a coalition.
As the House of Commons Library itself explains[0]:
"In 2019 the Conservatives got one seat for every 38,264 votes, while Labour got one seat for every 50,837 votes. It took many more votes to elect a Lib Dem (336,038) and Green MP (866,435), but far fewer to elect an SNP MP (25,883)."
(Note that the fact that the SNP are over-represented in Westminster is little comfort, given that they only field candidates in a minority of Commons constituencies, and I have covered the strength of their support in the Scottish parliament elections, with its different voting system, in another comment. Also, the SNP are principled enough to oppose FPTP despite the fact that they benefit from it in Westminster[1]).
To steelman your position a little, perhaps by "form a coalition" you mean some sort of electoral pact before an election. I mentioned in another comment that this has been tried in a few cases, but there are severe political problems with the idea of parties telling their candidates not to stand in specific constituencies, hoping that their voters will still bother to turn out and support the "second best" alternative. Not only is there no guarantee, under FPTP, that this strategy would work, but it would start to make a mockery of the idea of having political parties at all if some of them are actively avoiding standing candidates.
> You can look at them and call many of them 'left', but other than that they're not really compatible.
It's true that there are as many policies which divide these parties as unite them, but it's more accurate to say that a Principal Component Analysis would detect what we call the "political spectrum" of left and right wing parties as the most significant dimension of political opinion.
Just because you would need millions of political parties to fully capture all the individual political positions of every voter doesn't mean that there aren't broad trends, and in particular it is possible that a (weighted) random policy picked from a non-Conservative party could be on average more popular with the electorate than the equivalent Conservative party policy.
Ideally I would express this as candidates, parties, and voters in an n-dimensional space, so we could talk about drawing hyperplanes to define parliamentary majorities, but that's probably too abstract to be helpful. If you haven't played around with Nicky Case's "To Build A Better Ballot"[2], which helps visualise something similar in two dimensions, I highly recommend it.
> For example are the Liberal Democrats part of your left block that would win? But when given the choice they coalesce more readily with the Conservatives in practice.
We really only have one data point for how readily the Liberal Democrats form coalitions with different parties, and the specific political environment in 2010 is really not helpful to extrapolate that point from. Not only would Labour and the Liberal Democrats not have had enough MPs to hold a majority at the time, but the reputational damage of the coalition with the Conservatives has no doubt changed the political calculus that the Liberal Democrats would apply if a similar situation were to happen again.
> What vote do you think is being split? Some kind of generic not-Conservative vote? People vote for other parties - they aren't split among a vote not for the Conservatives.
I think there are a few factors that make things more nuanced than "People vote for other parties". As I mentioned in another comment, FPTP leads to constituencies where people feel that their vote doesn't count, so they either don't vote at all or vote for the "lesser of two evils", which both inflates the support for the Conservatives and also prevents new parties from gaining traction.
> If it really were simple vote splitting then coalitions would form, and they don't
That's a great point, but actually the UK has seen informal coalitions with parties standing down candidates in specific seats. This idea is so entrenched in British politics that it even has its own Wikipedia article.[0] The fact that the Conservatives have been the only major party since WW2 to form a coalition government is mostly due to the fact that in other general elections, the party with the most seats hasn't needed to form a coalition (perhaps with the exception of 1974), and it would make even less sense for the opposition parties to form one.
> Are the Conservatives and Labour splitting the not-SNP vote?
If you look at the 2016 Scottish Parliament election[1] (which uses a voting system that rewards honesty better), the Conservatives and Labour received 44.6% of the constituency vote, combined. That is less than the 46.5% that the SNP received. Even if you add the constituency vote share of the fourth largest party (by seats won), Scottish Green, they still don't match the success of the SNP. In any case, vote splitting is not such a concern under the Additional Members System.
> An absolute popular majority?
I apologise if my "51%" comment was unhelpful. You asked "How much more of a majority do you think it could possibly be?" and I wanted to highlight the fact that 43% isn't any kind of majority at all, but maybe you meant "plurality". In any case, I agree that it would probably be a bad sign if a party had a majority of the popular vote, and I would say it can also be a bad sign if a party gets a majority of seats without a majority of votes. Big parties effectively tend to be coalitions within themselves anyway, so I would prefer if the dynamics of those coalitions were played out on the national political stage, rather than as internal party scheming.
Perhaps you've heard of the problem of "vote splitting":
https://en.wikipedia.org/wiki/Vote_splitting
> How much more of a majority do you think it could possibly be?
Well, try 51% for a start.