It was a perfect May dawn, that moment 20 years ago when the scale of New Labour’s victory became settled beyond dispute. The beauty of the sunrise, the comprehensive wipeout of the Conservatives after 18 years, four defeats and a long and tightly choreographed election campaign produced a sense of euphoria. However hard Tony Blair and the people around him tried to suppress triumphalism, however cool the new prime minister sounded as he announced that he had been elected as New Labour and he would govern as New Labour, it seemed as if everything had changed, for ever. The Guardian reflected this enthusiasm: this election, the editorial at the time decided, “now joins 1945 and 1906 as the third great progressive electoral landslide of the 20th century”.

Like 1945, 1997 was a landslide that had been nearly a generation in the making. Labour had survived an existential struggle between social democracy and the Bennite left. And it had survived defeats – none more painful or damaging than Neil Kinnock’s unanticipated failure in 1992. The monstering of the party leader by the press shaped a party of extreme caution and obsessive media management.

But New Labour did not win only because of a well-constructed and lavishly funded campaign. It won because its architects –Tony Blair, Gordon Brown, Peter Mandelson, Philip Gould and Alastair Campbell – all paid attention to voters’ concerns and aspirations and shaped party policy to reflect and engage with them.

And they did change Britain. Literally, by devolving power to Scotland, Wales and London and bringing peace to Northern Ireland. Emotionally, by legitimising a sense of patriotism while engaging with Europe and reinventing international development. They extended gay rights and restored public services, reforming and investing in hospitals and schools, prioritising the fight against poverty and introducing the minimum wage.

But it is also true that the 13 years of New Labour did not transform the country as Attlee’s 1945 government had done. They left none of the radical and lasting institutional change. They did more to affirm than to challenge the Thatcherite idea of the smaller state, and they never did enough to challenge the supremacy of market forces. They inherited and exploited an exceptional period of economic growth, but also the rise of a new threat: global terrorism that led to the catastrophic misjudgment of the war in Iraq that overshadows the Blair years.

The 1997 victory was, as the Guardian described it at the time, a “vast public repudiation” of the previous Conservative government. But success can also blind the successful. New Labour should have paid closer attention to regulating the City. Its failure to do so contributed to the banking crisis, which in turn destroyed Mr Brown’s prime ministership. New Labour was relaxed about the complex mechanisms used in the financial world as long as bankers said they were playing by the rules. They were not, and nobody was checking.

Likewise it is easy to see now that immigration was a crisis acquired in a fit of absence of mind. The distributional effects of the policy, which has had a history of cultural convulsions, appeared ignored in favour of economic ones. This was a mistake, with profound consequences, as the Brexit vote showed.

The longer a party is in power, the harder it becomes to stay engaged with its activists. They are almost always disappointed by how little of what they care about gets enacted, and often offended by the lack of attention that their efforts attract from the top. No Labour governments, not even Attlee’s, have ever been anythng but a disappointment to the people who campaigned most passionately for their election. What continues to infuriate many party members today is that New Labour felt like “politics as usual” rather than a radical force: that it changed the party rather than the country. There is something in this: Mr Blair converted Labour to economic liberalism just as David Cameron converted the Tories to social liberalism. But after the economic crash, the accusation that New Labour would not stand up to powerful moneyed interests, mainly for fear of being considered anti-business, toxified the brand. Nor has Mr Blair been the best custodian of his own brand.

History may be kinder than today’s critics, in part because New Labour was a product of its time. But its failures jeopardised the alliance of progressive forces the party must now put back together to win again.