In last week’s Dutch general election, only 5.7% of the electorate voted for the Labour party; five years ago, its share was 25%. In France, opinion polls have the Socialist party’s presidential candidate averaging around 13%, compared with 29% in 2012. By such yardsticks, the UK Labour party’s 26% support level in this week’s Guardian ICM poll may not seem all that bad. If nothing else it is a reminder that Labour’s manifest problems are in some respects part of a more general slump and challenge for parties of the centre-left.

But not in all respects. Such a slump is not an iron law of history. There is nothing predetermined about the centre-left’s decline. In Germany, the return of Martin Schulz as the Social Democratic party’s chancellor-candidate against Angela Merkel has reinvigorated Europe’s most important centre-left party after a long period of decline; the latest Insa-YouGov survey has the SPD in the lead. In Portugal, António Costa’s socialist coalition government continues to defy the doomsayers; Mr Costa’s socialists are currently averaging 40% in the polls. It remains possible, both in theory and practice, for centre-left parties with the right combination of imagination, credibility and good leadership to turn events in their countries to political advantage even in tough times. That ought to be happening in Britain with the Labour party. It palpably is not.

This week’s Guardian-ICM poll spelled out the scale of the problem facing Labour. The Conservatives have a 19-point lead. If it was not for the standard ICM adjustment – which is designed to take account of the “shy Tory” factor – Labour would have recorded its worst score ever in the series. Almost every demographic prefers the Tories to Labour – by 41% to 29% among supposedly more leftwing 18- to 24-year-olds, with even unskilled manual workers in the DE grades tied. Labour prides itself on its principles, but the Tories are seen as the more “honest and reputable” party. Theresa May and Philip Hammond have a 33-point lead on economic competence over Jeremy Corbyn and John McDonnell – an increase on their pre-budget advantage.

This last fact ought to flash a particularly bright warning light for Labour. Two weeks after a lacklustre budget whose most headline-grabbing measure fell apart within days, with the prime minister slapping down the chancellor, Labour has not dented the Tory lead at all. On the contrary, the lead has increased. On Tuesday inflation ticked upwards to 2.3%. Prices are now on a par with wages across the economy as a whole. This almost certainly marks a crossover point. Real incomes seem set to decline in the months ahead. This ought to be a moment for the opposition to hold the government’s feet to the fire. Instead, Mrs May commands the political landscape with ease.

So what is Labour doing? As Britain heads for the EU exit door and Labour loses a byelection in a seat it has held for more than 80 years, much of its energy is focused not on the government but on its own factions. Mr McDonnell says the Labour right is attempting a soft coup. Tom Watson, the deputy leader, accuses Momentum and Unite of taking over the party. The hard left is the scene of bitter infighting. Unite’s Len McCluskey accuses Mr Watson of skullduggery, which is a fine charge from someone who didn’t need to put his union through a premature leadership contest. Labour seems bent on rerunning to the 1980s, only this time with the unions and the party’s big figures lacking the heart, the curiosity or the heft – and the command in Scotland – to pull it around.

Labour isn’t necessarily in terminal decline. A quarter of voters still support it. But the decline is enormous and it can’t go on like this. Labour needs to revitalise its vision and values, rebuild a coalition of interests and find leaders to start turning the current failure around. It won’t do that by obsessing over internal issues. It requires a massive change of direction at the top. Right now, though, Labour simply isn’t up to the job.