What is important is not that George Galloway won the Bradford West by-election but that Ed Miliband had no idea he was going to. More the Bradford Surprise than the Bradford Spring. Not that I knew any better. Like most Westminster journalists I was having too much fun thinking up pasty-related puns and accusing David Cameron of being "out of touch" to be in touch with the voters of a northern city.

It is embarrassing as a journalist to realise how much one is dependent on sources in the main parties for information about what is happening in places such as Bradford. Nobody at the top of the Labour Party was worried about the by-election and so, even when the bookmakers said that they had taken several large bets on Galloway on polling day, I ignored what should have been primary evidence. I may have been guilty too of letting what ought to be influence my perception of what is, having been glad to see the back of him as an MP in east London.

More fool me. But how much more worrying for Miliband that his party did not see it coming. I am not saying that Labour should have held the seat, or that it would have done had it had a better organisation or a better leader. But if it had a better organisation it should have known what was about to hit it. The spin-doctorate could at least have prepared us for the singular phenomenon that is Galloway, once again feeding off the feeling of victimhood of many Muslims, and the different feeling of victimhood of some of the white working class.

Instead, Labour thought it had pre-empted trouble by holding a quick by-election. Its operation in the constituency must have been moribund indeed if it failed to pick up the warning signs and relay them to head office. Meanwhile, the staff at HQ have been furious in semi-public over a mishandled reorganisation.

Despite the Government's post-Budget slapstick comedy and Labour's 10-point lead in the opinion polls, the party feels empty and demoralised. At some level, most of the party knows that a bit of disarray in Downing Street and a mid-term opinion-poll lead is not enough to win.

A fuel crisis did not amount to much when the pumps ran dry in September 2000. William Hague went into the lead in the polls for nine days, but sympathy for the pickets evaporated, the tankers rolled, everything went back to normal and Tony Blair won a second election the following year by the same margin as the first. This time, the flow of fuel has not even stopped, there is no strike, and the whole thing will be forgotten faster than Hague's leadership of the Conservative Party.

The nonsense about VAT on hot takeaway food will also fade quickly. It is important only because it signifies a bad Budget. It – and the granny tax – came about because David Cameron, George Osborne and Nick Clegg were distracted by the cut in the 50p top rate of income tax. They were right to be, because that was a real mistake, not mere media froth. Last weekend's sting by The Sunday Times against Peter Cruddas, the Tory party co-treasurer, was another Westminster frenzy, but it also matters because it further identified the Tories as the party of the rich.

Against that, a by-election defeat that should not have come as a surprise is not important. Galloway has been an MP before and made no difference to anything much. But if Galloway's win does not matter in itself, it does, beyond exposing the weakness of Labour's organisation, remind us of two things.

One is that large numbers of people feel voiceless and excluded by main-party politics. Ruthless populists can use the politics of identity (nationalism or religion) to pose as insurgents and win elections. That might make a difference in Scotland: senior civil servants in London think there is a 50-50 chance that the Union will break up.

But Gallowayism is a dead end. There is only one other constituency with as high a proportion of Muslims as Bradford West and Galloway's previous seat, Bethnal Green and Bow, and that is Birmingham Hall Green. There, Salma Jaqoob, the titular leader of Galloway's Respect party, got 25 per cent of the vote at the last general election.

The other lesson of Bradford West is that predicting elections is a mug's game. As a mug, however, I can predict that Labour will do well in the local elections next month – except in the London mayoral contest. Most of the local council seats up for election were last contested in 2008. The BBC calculates that Labour's national equivalent vote share then was 24 per cent, when the Tories had 44 per cent and the Liberal Democrats 25 per cent. In the game of managing expectations, though, disproportionate attention will be paid to Boris versus Ken. And that is a game Ed Miliband has already lost. The one thing worse for him than the Labour candidate being defeated would be if Ken Livingstone, with his Galloway-lite sectarian politics, were to win under a Labour banner.

But the unpredictability of elections cuts both ways. David Cameron never expected, when he proposed directly elected police chiefs and more city mayors, that Labour candidates would look like sweeping the board. And Miliband must be relieved that there is only one George Galloway, because there will be a rash of by-elections later this year. Liam Byrne and Gisela Stuart may stand down to contest the mayoralty of Birmingham, and Tony Lloyd and Alun Michael are standing down to stand as police commissioners.

By reminding us of the alienation from politics of so many voters, and of the unpredictability of elections, Galloway has performed a public service. And those are words that I never thought I would write.

independent.co.uk/johnrentoul; twitter.com/JohnRentoul