Cast your mind five years back, to the summer of 2010, when 50,000 students descended on London to protest the rise in tuition fees. They caused literal and political damage, forcing the government on the defensive and causing incalculable harm to the Lib Dems. Where is that student movement now?

It died a predictable death. The fact that legislation passed anyway and students got bored didn’t help, but it’s rarely discussed how quickly the movement fizzled out. Activists became beset by infighting, got burnt and left; there was no firm strategy beyond protests (as Paul Mason noted too); and momentum was lost due to a mix of timing and organisational failure. Activists said ousting NUS leader Aaron Porter would re-energise them but it barely stopped the downward spiral because he was never the real problem.

Over the last five years this cycle has been repeated several times. Leading activists at UKuncut told me the most vicious criticism they got came from hard-left & libertarians. The student-union occupiers, Occupy London and anti-austerity groups went the same way, fizzling out after infighting and lack of direction. I’ve met numerous activists since 2010 who stopped getting involved after exhaustion from arguments and accusations. As the disintegration played out in real time, those who questioned futile tactics were shouted down or driven out.

The left can be a powerful and influential force, as recent movements across Europe and South America have shown. But I’m not going to sugar-coat this because it wasn’t just Labour that lost miserably last month, and no amount of inspiring slogans or ‘retake-the-streets’ cliches will help unless we talk about this.

The British left has been an embarrassing failure over the last five years, for reasons that are entirely obvious. Again, I’m not courting popularity by writing this column, but the defeat of May 2015 will mean that another generation of activists will spring up to fight the Tories and their cuts. I would only hope they avoid the mistakes made from 2010 – 2015… mistakes that I also made or contributed to.

1) Focus on building long-term infrastructure not transient networks

Online networks are easily built and can be extended across the world while being quick and cheap. But the left can only succeed by building long-term infrastructure with mass-appeal. The Trade Unions and the Labour Party are perhaps the best examples but there are also many NGOs and charities that would fit the bill. Not much like that has taken shape over the last 5 years, other than perhaps 38 Degrees and Change.org – both of which were based on US models.

By definition, building sustainable groups with broad appeal would require a) more moderate language, b) working with people we disagree with c) refraining from purity tests, d) looking at funding options. There’s no other way around this. We can only shift the public debate by building infrastructure that is open to everyone.

2) Stop aping UKIP

UKIP thrive with a language of victimhood and by painting the world as black or white: ‘You’re with us or against us’, or ‘they’re all the same’. They don’t do nuance or evidence based policy. We cannot be like this; we have to be positive and life-affirming and we have to accept the world is a complicated place.

The last five years have consistently seen lefties claim: ‘they are all the same’ – when this wasn’t remotely true. Commentators such as George Monbiot, Frankie Boyle and Mark Steel hailed the SNP as revolutionary while saying Labour offered the same as the Tories. But the opposite was true: the SNP manifesto was near-identical to Labour’s, which in turn was vastly different to Tory plans. And yet, much of the left commentariat only focus on facts when arguing against Tories or UKIP.

As I’ve said before, this is anti-intellectualism on an epic scale. It’s the type of cliche politics the right excel at. But in the same way that Russell Brand’s revolutionary zeal collapsed after one interview with Ed Miliband, much of the commentary didn’t stand up to scrutiny. It isn’t just misleading, it’s destructive.

3) End the ambivalence around voting

We rightly complain that a growing share of Britons aren’t voting. Yet we fuel this very trend by being ambivalent about voting. Russell Brand argued loudly against voting and many on the left cheered him, only to watch an embarrassing u-turn days before the election. The Revolution ended in a farce.

Our Parliamentary democracy isn’t even close to being fair, but that won’t be changed by disengaging. Older Britons now form a disproportionately large share of voters and the policies our politicians pursue reflect that. There should be no ambivalence about a right that people died for, and any suggestion that ‘there is no one to vote for’ should be called out as ridiculous.

The left keeps losing because young people don’t vote. Don’t whine that there isn’t enough choice – there clearly is – instead we need movements to mobilise and register younger voters. Without that we remain a movement that whines from the sidelines.

As Podemos’s Pablo Iglesias pointed out, “politics has nothing to do with being right, politics is about succeeding.” We cannot even begin to talk about a fight-back without an acknowledgement of how so much energy, people and movements ended up crashing and burning. We can only succeed by learning from our mistake