Your party is tearing itself to shreds in the aftermath of a shocking defeat. Ideological division threatens to wreck all attempts to make progress. The electorate, always possessed of a keen sense of smell, detect a strong whiff of failure about your people and your brand.

What to do? Call in your most successful former leader, of course: they will remind everyone of a winning formula and end the madness.

That was the thinking behind putting Margaret Thatcher on stage at the Conservative conference in 1998 (though as this clip shows the decision to invite Ted Heath along too backfired somewhat). She was a serial winner, inextricably bound up with glorious victories.

No-one expected an instant return to success, but they might have hoped that, Tobruk-like, such a rallying round might signal the end of the beginning of the struggle back to power. It wasn’t even that. There were 12 long years of Opposition still awaiting the Conservatives before they could return to Government.

Not for the first time this summer, Labour would do well to study those grim Tory years. While the Left are right to observe the modern Tory determination to win, and the recipe for doing so, they often forget that it is born of long years of losing. We never came close to electing a Jeremy Corbyn, but we have already made plenty of the other errors Labour are currently committing.

Tony Blair’s speech today will fail to turn his party round for the same reason that Thatcher’s loyal support after 1997 failed to put us back onto winning form. It isn’t that his formula is incorrect – indeed, the likelihood is that the next Labour Prime Minister will reach Downing Street by pursuing exactly the kind of shift to the centre that he proposes. It’s that he is a titan of the past, not an active political player in the era in which he is trying to intervene.

In 2005, when Cameron (the fifth Tory leader Blair had faced across the despatch box) declared that “he was the future once”, he accurately diagnosed the condition – and, sadly for Labour, it is terminal.

Take the Conservative example again. There were innovations in policy, in campaigning, in party structure and so on between 1997 and 2010 which helped return our party to power. But it’s no coincidence that victory only came when the notorious Big Beasts of the 1980s were mostly out of the picture – Heseltine, Tebbit, Thatcher et al had all taken a back seat by 2010. (Ken Clarke carried on rather longer but that brought its own problems with his disastrous attacks on UKIP during the last Parliament.) Their party was able to breathe and grow in its own way, without the baggage that even a hugely successful career can bring with it.

Politics is simultaneously a process of attrition and accretion. One’s appeal wears off – as Thatcher found by the time of the Poll Tax, and as Blair experienced in his early years as some of his 1997 voters that it was all just spin. At the same time, one picks up problematic labels – some of those who voted Tory in 1979 were deterred by the industrial battles of the 1980s, while Blair shed plenty of votes as a result of Iraq. Both processes blunt the effectiveness of a leader, any leader, as time goes by.

For that reason, political leadership is a one-time experiment. In every parliamentary term the electorate learn and evolve. The wild optimism surrounding the 1997 campaign could not be repeated in our more sceptical age (for a start, D:Ream would refuse permission for Labour to use “Things Can Only Get Better”). The feeling of an existential socialist threat had a hold in 1979, after the winter of discontent and with the Soviet Union looming, that it could never have had even in the post-crisis turmoil of 2010.

Victorious former leaders deserve appreciation from their parties; it would be wrong and unwise to forget their achievements. But while their greatness may linger, that does not mean they are able to win any more victories.

Perversely, it may instead fall to Gordon Brown – a man untarnished by victory or popularity – to save his party from its madness. While Blair’s performances have the nostalgic air of a Las Vegas greatest hits show, Brown’s outing in Scotland last year displayed some of the desperation and grit of a pub rocker who still wants the break he never really got. To the Labour Party of 2015, the latter may feel more relevant.