‘Occasionally late at night at a Labour Party conference … the cry can still be heard. “Where,” a plaintive, maudlin voice will ask, “did it all go wrong?”’

So wrote the future New Statesman editor Anthony Howard in 1963. Then a rising star of political journalism, Howard had a confident answer to this melancholic cry - things went wrong for Labour on 26 July 1945, the day the party was elected to power on a landslide. Surprisingly, perhaps, for modern readers, the reputation of Clement Attlee’s government at that time was pretty poor. So far as many Labour party activists were concerned, Attlee’s was a record defined by compromises, lost opportunities and what was by the early 1960s an apparently unending period of Conservative rule.

Or perhaps it should not surprise. It is now 20 years since Tony Blair led Labour to another of the party’s rare landslide victories. And it is striking how this disregard for Attlee’s achievements finds an echo in how Jeremy Corbyn supporters regard the government elected on 1 May 1997. Some even believe Labour’s present troubles began on the fateful day Blair entered Number 10. As poet Michael Rosen has put it, since 1997 it has all been downhill, the Blairites having lost Labour over five million votes. According to the Corbynites, Labour will only recover once it rediscovers its pre-Blairite "socialist" self and puts 1997 behind it.

If a majority view amongst its members, the party’s few avowed Blairites naturally look on matters differently. Labour in 1997 after all enjoyed a 10.2 per cent swing from the Conservatives and won its biggest ever Commons majority, laying the foundations for an unprecedented 13 years in office. This was, according to columnist John Rentoul, because Labour discovered "the eternal verities of the Blairite truth". If matters subsequently went awry, it was only because Labour cast this truth aside by abandoning the centre ground. If the party is to revive, such Blairites believe it needs to return to the strategy that gave it 1997.

Such dichotomous views reflect the entrenched ideological positions in a party both deadlocked and in decline. As a historian of the Labour party and curator of an exhibition marking the 20th anniversary of the election I have my own thoughts as to which lessons the party should draw from 1997. They are ones neither side in the party may find of great comfort.

1. Winning involves waiting

The most depressing lesson for the party is that Labour only wins a working Commons majority after a prolonged period of Conservative rule. True of Blair in 1997, it is equally so of Attlee in 1945 and Harold Wilson in 1966. If there is any good news for Labour in this, it is that the Conservatives have already been in office for seven years; the bad news however is they’re probably less than halfway through their term.

2. Trouble for Conservatives ≠ Labour victory

But if all Conservative governments eventually come to an end, a long-serving Tory administration – even one in deep trouble - is only a precondition for a Labour victory, not its guarantee. Facing a divided Conservative party in office for 13 years, in 1992 Neil Kinnock expected to win. The country was after all in the midst of a recession and John Major’s government was divided over Europe. Yet Labour lost because those whose votes the party needed to win still felt the party was a worse bet than the Conservatives.

3. Offer hope - and reassurance

To win, Labour needs to primarily reassure voters while also offering them some hope. Hope without reassurance does not work. That was why Blair closed down what was traditionally the Conservatives’ most effective avenue of attack on Labour by, most famously, promising to not raise the top rate of tax. So when Central Office warned: "Britain is Booming. Don’t Let Labour Blow It", the slogan had little impact (a similar warning about "Labour’s Tax Bombshell" helped sink Kinnock). This meant that, having lost in 1992 in the midst of a recession, in 1997 Labour paradoxically won during a period of economic growth. But Labour also promised "Things Can Only get Better", that schools and hospitals would improve, while the young unemployment be helped into work. Gordon Brown, the New Labour Chancellor, called Labour’s approach "prudence with a purpose", although it was prudence rather than its purpose the party emphasised in 1997.

4. Know what victory is for

In 1997, Blair pursued one of the most cautious electoral strategies in living memory, one that met with spectacular success. But this led to caution in office. "We have been elected as New Labour," Blair declared, "And we will govern as New Labour." However, even those closest to the new Prime Minister hoped the strategy that underpinned 1997 was part of a process rather than an end in itself.

Writing in 2005, Peter Hyman, who advised and wrote speeches for Blair, argued Labour no longer needed to reassure voters and should start to actively create a "modern social democratic country" by arguing for higher taxes as well as for greater tolerance for minorities and more opportunity for those denied it. Blair had however created a prison for himself. He feared the electoral consequences of such a departure from the strategy that brought him his landslide. So, by the time Labour said it would raise the top rate of tax, it was to help pay for the bailing out of those banks which nearly collapsed during the 2008 financial crisis.

5. Neglect breeds enemies

Be nice to people on the way up, as you’ll meet them on the way down when your victories eventually give way to defeat. In the run up to 1997, Blair took the party with him, but only because he looked like a winner and Labour had been out of office for so long. If nearly 60 per cent backed Blair as leader in 1994 and a similar proportion endorsed his 1995 revision of Clause IV, many retained serious reservations. But instead of trying to keep the party on board, Blair urged the horses ever onwards. Like all Labour Prime Ministers before him, he ignored what was happening outside Westminster and Whitehall, in the constituency parties.

As Hyman argued in 2005: "We have to build a grassroots movement that will sustain New Labour in the long term. We have to use our powers of persuasion." But this was something Blair never seriously contemplated and nor did Brown. Jeremy Corbyn is the greatest beneficiary of this neglect.

6. Just surviving brings rewards

Time is a great healer. A recent YouGov poll revealed that Labour members’ favourite party leader is Clement Attlee. Even supporters of Jeremy Corbyn put Attlee second – after Corbyn. By 2017, the 1945 Labour government had become a thing of myth. Only its achievements, principally the National Health Service, are ever recalled.

Attlee started to come into fashion with the left in the 1980s. Overlooking how his 1940s counterparts attacked it for its moderation, Labour's in-house radical Tony Benn compared the party’s 1983 manifesto with the "openly socialist policy" put to the country in 1945. It might seem unlikely just now, but when Blair is long dead and nobody alive can remember 1 May 1997, some Labour radicals might find themselves invoking the "spirit of 97" and lauding the minimum wage, Sure Start and the £5bn windfall tax on utility companies that helped the long-term unemployed back into work. If Labour still exists then.

Steven Fielding is a professor of political history. He curated the 'New Dawn? The 1997 general election' exhibition, running at the People’s History Museum in Manchester between 25 March and 4 June 2017. Associated with the exhibition is the @newdawn1997 Twitter feed which reconstructs the 1997 campaign day-by-day.