In case you missed it on Thursday, my colleague Andrew Sparrow wrote this excellent guide to why these elections could be so transformative for British politics:

Earlier I said that today’s elections are likely to be seismic. (See 8.14am.) We don’t have any results yet, but unless all the opinion polls, and all the council byelections that have taken place over the past 12 months, and all the parliamentary byelections that have taken place since the general election, turn out to be completely unreliable guides to how people vote today, then we already have a rough idea of what the outcome will look like. It will be enough to transform the political landscape of Britain – in at least seven ways.

1) The full arrival of five-party politics in England

Two-party politics has been in decline in British politics for more than half a century. Its high point was in 1951, when 97% of people who voted in the UK general election opted for either the Conservative party or Labour. In recognition of the Lib Dems, people used to talk about England having a two-and-a-half party system. Scotland and Wales have had strong nationalist parties for years, and Reform UK easily won the English local elections last year. Under Zack Polanski, the Greens have now been soaring in the polls and this is the first English election where talking about “main” parties and “minor” parties no longer makes sense. (How can it, when the “minor” parties with least parliamentary representation, Reform UK and the Greens, have been the two best-performing parties in some polls?) Those terms describe the parliamentary situation but not politics outside, where five parties are competitive across England and it is probably more useful to think in terms of legacy parties and disruptor parties.

2) Reform UK’s emergence as a GB-wide party

When Nigel Farage was leading Ukip, it looked like an English nationalist party. Scotland seemed to have a healthy resistance to Faragism and on one occasion, in 2013, he had to be locked in a pub in Edinburgh for his own protection. The Brexit party also never really succeeded in Scotland (although it did make inroads into Wales), but under its new name, Reform UK, it is competing with Plaid Cymru for first place in Wales, and with Labour for second place in Scotland. It should easily win the English locals, and so it is the only party with a realistic chance of coming first or second in England, in Scotland and in Wales. That is why Farage is boasting about his being the “only true national party”.

3) Wales going nationalist

Plaid Cymru, the Welsh nationalist party, is widely expected to be the largest party in the Senedd after the elections and, unless Labour and Reform UK form some extraordinary version of their own Molotov–Ribbentrop Pact, Plaid will be the only party with a realistic chance of forming a government. Rhun ap Iorwerth, the Plaid leader, would be the first non-Labour first minister of Wales since devolution. Assuming the SNP remain in power in Scotland (almost certain), and with Sinn Féin the largest party at Stormont, this would mean nationalists leading the three non-English nations in the UK.

This does not mean Welsh independence is on the cards. Although formally committed to independence, Plaid has never given any serious thought to how independence might be achieved and a government that tried to implement it would find it even more complicated and less popular than the project has been in Scotland, where independence was rejected in a referendum in 2014. But, after that vote, the Scottish parliament got new powers, and the Scottish government started to use them to diverge from UK government tax policy. The Welsh government has fewer devolved powers than its Edinburgh counterpart, but with Plaid in power in Cardiff over time that may change.

4) Labour support collapsing – especially in London

If Plaid win in Wales, it will be the first time Labour has lost a big election there for more than 100 years. It is also expected to lose big in London, where it is the dominant party in local government and where at the last election it won 59 of the 75 parliamentary seats. In fact, it is on course to do badly everywhere, recording its worst result since at least the 1970s. Here is the forecast from Britain Elects, who produce election forecasts for the New Statesman and who have a good record.

Tomorrow you may hear talk from Labour figures of the 1968 London elections. Taking place after devaluation the previous year, they were an utter disaster for Labour, which lost 17 of the 20 boroughs it controlled in the capital. They almost all went Tory. The upside for Labour people looking for a positive message out of this today is that the party recovered and, two years later, Harold Wilson called a general election that he thought he might win. But he lost. And Wilson did not have to contend with Reform UK, or the Greens, or five-party politics, or prolonged austerity, or social media, or any of the other factors that make Starmer’s situation different.

5) Local government getting more pluralist

Local government in Britain used to be dominated by the two biggest legacy parties, the Conservatives and Labour. That picture should take a considerable jolt this weekend. The Liberal Democrats think they will be at least the second largest party in local government by the time of the next election, in terms of councillor numbers, and perhaps even the biggest. And Reform UK and the Greens will have a signficantly bigger presence. This chart, from an excellent preview of the elections by Dylan Difford on Substack, shows how councillor numbers have changed over recent years.

And Open Council Data has full figures.

6) Failure of first past the post

It is increasingly clear that the election system used in UK parliamentary elections, and for local elections in England and Wales, does not work in five-party politics. It functions well for two-party politics, but in multi-party politics it can easily lead to a party winning a far larger proportion of the seats than it merits based on the proportion of the votes it won. This famously happened at the last general election when Labour won 34% of the vote but 63% of the seats. Less well known is how this is increasingly happening at local authority level too. Rob Ford has also written a terrific Substack guide to the elections, and he includes this chart showing how in some cases last year Reform was winning three-quarters of the seats on a council with less than half the votes. Ford says:

The crucial question for the Greens this year, as for Reform last year, is whether they can push their support in target areas above the ‘tipping point’ where first past the post goes from sandbag to springboard. For Reform last year, as the graph below illustrates, that tipping point came around 30% – in councils where Reform won above 30% they were generally over-represented in seats, often taking huge majorities.

The Guardian has an editorial today saying this system must change.

7) Labour’s fightback challenge

We don’t know yet how Labour will react to the results. Keir Starmer may face a leadership challenge. Even if he doesn’t, the party is going to have to come up with a response that goes beyond ‘Keep calm and carry on’. Elections function as transmission mechanisms; they deliver blunt messages to government and – unless the polls are 100% wrong – the message tonight will be that something needs to change.

So it will.