First past the post is a curious electoral system. On the surface it’s simple – most votes wins - but when you aggregate 650 local results into a national outcome it can produce a Parliament very different to the national shares of each party’s votes.

Famously, in 1983 Labour’s 28% gave it 209 seats whilst the Alliance, only 2% behind, won just 23. In 1992, John Major won 42% and 14m votes (the highest ever) but only a majority of 21.  Most egregiously of all, in 1951 Labour secured 49% of the popular vote – yes, 49 – and…. lost, with Winston’s Churchill’s Conservatives securing a majority of 16 on a smaller vote share. Imagine the outrage if that happened today? What would have happened to these governments had their majority better reflected their vote share?

This phenomena might be about to happen again. Because whilst all the talk is of Labour riding high, the reality is that almost every poll shows their support slipping a little.

YouGov last week showed Labour on 37%, their lowest with the pollster since summer 2022, but suggested that because of the huge split on the right (with the Conservatives on 18% and Reform on 19%) this modest winning vote share would deliver the biggest majority in British electoral history, somewhere in excess of 200.

In the last two elections, Boris Johnson won with 44% in 2019 and Theresa May clung to power with 42% in 2017. It’s less than the 40% Jeremy Corbyn won against May. What happens if Keir Starmer wins a massive, historic majority on a relatively low vote share?

On one level, it doesn’t matter. The majority is the majority. If Starmer has a majority of 200 he will never lose a vote in the Commons. He can do what he likes, and the Labour Whips will make sure it gets through the House.

But politics is never quite as simple as that. It’s also about an emotional contract with the country and if only 37% of the country has voted for you (and once you factor in those who don’t vote, it will only be about one-in-four adults voting Labour) then that contract is weak. You risk being a high-majority, but low-mandate government.

In that scenario the Left would never tire of pointing out Starmer won fewer votes than Corbyn in 2017, and demand greater radicalism. On the other hand, restraining any radicalism, will be the House of Lords – where the Conservatives will remain the largest party. Peers will regularly point to the lack of mandate to resist anything which goes beyond the modest ambition in Labour’s manifesto.

Parties have won a majority with less than 40% of the popular vote three times. Harold Wilson’s win in 1974 heralded five years of weak government culminating in the winter of discontent. Tony Blair only lasted two years after his sub-40% 2005 win. And David Cameron’s win in 2015 kicked-off a decade of chaos. Notably, in none of these cases did the party leader last more than two years after the election victory.

Of course, Starmer as a new PM will start in a better place than any of Wilson, Blair or Cameron.  No one imagines he won’t last a full term. But the seeds of downfall almost always lie in the birth of success.

Starmer does much to emulate Blair. But if he wins a 1997-style result from 2005-levels of enthusiasm, it will have big consequences through the life of his government.

(Photo provided by Sky News)