I am not sure I've ever mentioned this publicly before. I am still a bit embarrassed. But I am revealing it now because I need you to understand that I speak from a position of authority. It was my job to stop the chicken defecting to the Labour Party.

In the 1997 campaign as the Tory Government began to sink beneath the waves, we advisers met daily to plan the rearrangement of the deckchairs. Someone (else) came up with the bright idea of hiring an actor to dress up as a chicken and follow Tony Blair around.

Surprisingly, the chicken's appearances failed to improve our poll ratings in the way we had anticipated. And then a rumour began to swirl around Conservative Central Office - the chicken had doubts. He was thinking of coming out for Labour.

For the rest of the campaign, it became my job to buy the chicken lunch, empathise with him about the difficulty of finding jobs in the theatre and make sure he fully appreciated that new Labour would mean new danger. We may have suffered a landslide defeat but I am proud to say that we did so with all the poultry still on side. I miss our lunches, actually. I wonder what the chicken is up to now.

This all came back to me when reading about the Crewe & Nantwich by-election. Labour has sent up a couple of young men dressed as toffs to follow the Conservative candidate around. It has not boosted its opinion rating either. And now it seems as if one of these men went to an expensive public school himself (not the same posh school as Ed Balls, a different posh school). You have to hand it to Gordon Brown's crack team. I didn't think it was possible, but they've done it. The toffs stunt is stupider than the chicken.

The chicken simply made us all look childish and a bit desperate. To this the toffs stunt, personally approved by Gordon Brown, adds another dimension - it is an abandonment of one of the party's most attractive features.

I know where Labour got the idea that campaigning against David Cameron's class might work. It came from a group of pundits I call the ChipOx Club. These are journalists who went to Oxford from middle-class homes. On their way back from the library to their college rooms in Michaelmas term, carrying a cup of cocoa and determined to finish their essay on the Battle of Naseby, they had champagne spilt on them by the drunk younger son of an earl who was fleeing a shaving foam fight. They have hated toffs ever since. And they are convinced that everyone else shares their dislike.

As a Jewish suburbanite and the son of immigrants, I have always found such class prejudice baffling. But as a political analyst I have this further observation - if you are going to campaign in Crewe on class, the toffs are the wrong class to campaign against.

Since the days of the industrial revolution there has always been something of an alliance between the working class and the aristocracy, united against the common enemy - the mill owners. When the fighting broke out in the streets of Leeds over the amelioration of factory conditions, radicals and workers' leaders such as Richard Oastler saw themselves as allies of Tories such as the Earl of Shaftesbury.

To be portrayed as a top-hatted toff actually represents an improvement in the Tory image. Being seen as pinstripe-suited bosses, estate agents and spivs was far more devastating. Consider the brilliant salvo fired at the US presidential candidate and businessman Mitt Romney by his opponent Mike Huckabee: “People would rather elect a president who reminds them of the guy they work with, not that guy who laid them off.” This is the sort of sentiment that has the ability to damage the Tories. Toffs are benign and reassuring by comparison.

If Labour is baffled by its failure to make class work against Mr Cameron, I think this is part of the reason. His class background is actually helping him to change the way people see his party in a positive way.

There is, however, another reason that it isn't working. Voters do not use Labour's campaign to help them to understand the Tory party. They understand that one party isn't likely to give them an honest picture of the other. They use Labour's campaign to help them to understand the Labour Party. And what the Crewe campaign is doing is signalling that Tony Blair's Labour Party is dead and another, much less attractive, organisation has replaced it.

In 1976 Labour ran a party political broadcast attacking the “honourable Algernon” who was born “with a silver spoon in his mouth”. Even at the time, more than 30 years ago, this was regarded as disreputable. Jim Callaghan, then party leader, disowned it. But some in the party hierarchy regarded the broadcast as a masterstroke. Mr Blair built his career on an understanding that these people were wrong.

Class warfare, even if waged against someone else's class, is spectacularly unattractive. It makes Labour seem aggressive, prejudiced, an exclusive sect more interested in your background than your ideas. Mr Blair wanted his party to be a big tent, welcoming everyone. This idea, this powerful political idea, which brought the Tory party to the edge of extinction, which brought landslide Labour majorities, is now over. And with it Labour's political hegemony.

New Labour is dead. Gordon Brown has killed it. And at the funeral, the undertakers will be wearing the top hats from the Crewe & Nantwich by-election campaign.

daniel.finkelstein@thetimes.co.uk