Andy Burnham's victory in the Makerfield by-election represents a remarkable personal success.
Last year in the Runcorn by-election, Labour's vote fell by 14 points. Four months ago in Gorton & Denton, it collapsed by 25 points.
In Makerfield itself, Labour were 20 points behind Reform in the local elections on 7 May.
Even at the best of times, support for the party of government nearly always falls in by-elections. Yet, in yesterday's ballot, Burnham not only retained every bit of the 45% share of the vote Labour won in the seat in 2024, but actually pushed his party's share up by 10 points.
With Labour stuck at just 19% in the national polls, much as it has been ever since last autumn, there has been no evidence of any marked change in Labour's popularity in the last few weeks to account for this turnaround.
Indeed, Labour saw its vote fall heavily in both the Scottish by-elections also held yesterday – by 19 points in Aberdeen South and 18 points in Arbroath and Broughty Ferry.
Moreover, polling conducted during the Makerfield campaign suggested Labour would have lost quite badly if anyone other than Burnham had been Labour's standard bearer.
There appears to have been two key foundations to Burnham's success.
First, he managed to persuade many of those who voted for the party in 2024 to return to the fold. Polls published last weekend suggest that four in five of those who backed Labour two years ago voted yesterday voted for Burnham.
In contrast, the national polls suggest that only a little over half of 2024 Labour voters are currently minded to vote for the party again.
Second, as the polls also anticipated, Burnham seemingly benefited from a squeeze on the Conservatives, the Liberal Democrats and the Greens. They won just 3% of the vote between them, down 19 points on 2024.
The 0.4% won by the Liberal Democrats represented their worst ever by-election performance, while the 2.2% won by the Conservatives was only marginally better than the all-time low of 1.9% recorded in Gorton and Denton four months ago.
Both patterns were probably occasioned by a mixture of motives.
Some people will have voted tactically to keep Reform out, some will have been hoping to bring about the downfall of the prime minister, while others will simply have been persuaded by Burnham's personal style and his record as Greater Manchester mayor.
Meanwhile, Makerfield should have been prime territory for Burnham's principal opponents, Reform. The party's support is heavily concentrated among those who voted for Brexit 10 years ago, and as many as two-thirds of voters in Makerfield voted Leave in the referendum.
Failure to take the seat will thus be a particularly bitter blow for Nigel Farage.
His party's support was up by just three points on 2024, well short of the 21 point increase it registered in Runcorn and the 15 point rise it enjoyed in Gorton and Denton, as well as the 12 point increase it currently has in the national polls.
At the same time, the by-election campaign saw emerge from the shadows another new challenger - Restore Britain, the breakaway party founded by former Reform MP Rupert Lowe, that is campaigning for an even tougher stance on migrants than that advocated by Reform. It was the only party other than Labour and Reform to keep its deposit.
How many of the 7% who voted for Restore might otherwise have voted Reform is difficult to tell. But Farage will certainly not welcome the emergence of competition for the support of pro-Brexit, socially conservative Britain that Restore – currently running at 3% in the national polls – potentially represents.
But if the Conservative vote collapsed in Makerfield, the very opposite happened in Aberdeen South.
In a city that was once made rich by oil but which has now fallen on harder times, the party turned the ballot into a referendum on the net zero policy of both the UK and the Scottish governments.
It was rewarded with a 25 point increase in its share of the vote, a record for the party in a post-war by-election and its first by-election gain in Scotland since 1967.
Last night's by-elections will reverberate around Westminster for a long time.
A challenge to Sir Keir Starmer's tenure of at Number 10 now seems inevitable. But just as importantly, the government's energy policy could well now find itself in the midst of a serious political storm.
John Curtice is professor of politics at Strathclyde University, and senior fellow at National Centre for Social Research and 'The UK in a Changing Europe'.
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