Enjoy your victory, Sir Keir – the really bad news is you’re heading to No 10

Even if we take Keir Starmer at his word and assume that Labour is serious about refusing to be complacent about the general election, it is now hard to see what is going to prevent him from taking office with a decent parliamentary majority by the end of the year.

Starmer can try to play down the significance of Thursday’s double by-election win. The second-best ever swing to Labour from the Conservatives in Wellingborough, 29 per cent, was a freak result, he could say, because the local Tories chose the girlfriend of the disgraced former MP as their candidate.

Look at Kingswood, he could say. There, the swing to Labour was a merely respectable 16 per cent. Go and read Peter Kellner, he could tell his shadow ministers. The former president of YouGov said: “Labour’s two victories were far more the product of Conservative weakness than Labour strength.” In Kingswood, Labour didn’t do as well as it did in other by-elections last year: Selby (24 per cent swing), Tamworth (24 per cent) and even Mid Beds (21 per cent), where it was fighting off a strong Liberal Democrat challenge.

Also: beware the Green vote, Starmer could say. In Kingswood, the Greens doubled their share of the vote to 6 per cent. The Lib Dem vote may be squeezable – they lost their deposits in both seats – but the Greens are coming at us from the left and they won’t be swayed by arguments for tactical voting.

Unfortunately for Starmer’s “no complacency” message, his shadow cabinet are unlikely to be taken in by such extravagant pessimism – even if pessimism is something they have grown used to over the years.

They know that a 16 per cent swing in a by-election is enough to win them a general election. It slightly outperforms the current average in the opinion polls, which suggests a 15 per cent swing since the last election. And they know that, now that Scotland has fallen, a swing half that size would be close to producing a majority Labour government.

Nor are they likely to be too scared by the threat from the Greens. The Green candidate did all right in Kingswood, on the outskirts of Bristol, which is the Greens’ second city after Brighton, but the party bombed in Wellingborough. The Green threat to Labour is nothing compared with the Reform threat to the Conservatives. Reform did well in the by-elections, proving that its opinion poll rating is real enough. It is likely to fall back in the general election but will probably gain enough votes at the Tories’ expense to hand Labour 20 seats or so.

No wonder Starmer didn’t take himself at his word, and went on a victory lap this morning, telling TV audiences: “The country is crying out for change.”

What is certainly true is that the by-election wins – and Thursday’s GDP figures showing Britain was in a recession – have wiped out memories of the difficult start to Starmer’s week. The row about Labour’s candidate in the next by-election, in Rochdale in two weeks, probably hardly registered with most voters. But there will be plenty of chances to remind people of the reasons that positive enthusiasm for Labour is in short supply.

When the Rochdale by-election happens, the messages from the formerly safe Labour seat will be as awkward for Starmer as this week’s were favourable: that Labour chose a dud candidate; that the party’s antisemitism problem is not fully uprooted; and that the leader’s stance on Gaza is causing problems with large parts of the party and its voters.

George Galloway will be out and about, which can never be a good thing for Labour; Simon Danczuk, the former Labour MP who is the Reform candidate, will be attacking the party from the right; and Azhar Ali, the disowned Labour candidate, might still win because it was too late to take his name and party affiliation off the ballot paper.

After Rochdale, the normal run of Tory by-election defeats may resume. There may be a by-election in Blackpool South, as Scott Benton, the Tory MP, is facing a 35-day suspension from the Commons for appearing to offer to lobby ministers for payment.

Other things will go wrong for the government. Things will go wrong for the opposition too, but fewer people will notice them. The economy might pick up – indeed, it probably already has. The figures putting Britain into recession are out of date and the indicators might improve for the rest of this year. But people feel poorer, and Labour will hammer the r-word as a symbol of that for all it is worth.

The significance of this week’s by-elections, then, is that – whatever Starmer says about taking nothing for granted – they rule out any sign that Rishi Sunak can turn things around in the absence of war, plague or acts of God.

Rather than worrying about how they might lose the general election, Labour ought to be worrying about how on earth it can cope with winning it. It will inherit the public finances in a terrible state. Starmer and Rachel Reeves, the shadow chancellor, should not be fearful of 1992 or other elections that Labour lost. They should worry about 1929, 1945 and 1964 – elections that Labour won but after which the party trapped itself by sticking to the economic consensus and defending the value of the pound.

You are right not to be complacent, Keir – because you are going to win.