Jeremy Corbyn’s 2015 leadership campaign motivated thousands. Enthused by an unequivocal, principled call to build a fairer Britain and a more peaceful world, I was one of hundreds who joined volunteer phone-banking sessions. In Labour’s 2017 general election team, I played a small part in the by then huge movement which inspired millions to vote for the party and which has since inspired socialist parties across Europe and beyond.

Making a decisive break with lowest common denominator politics, calling out austerity as a political choice and not a necessity, our reinvigorated party has forced cracks into the consensus supporting neoliberal economics worldwide. It has helped to restore the fight for social justice to the heart of left politics.

Labour has been bold, unapologetic in its defence of the marginalised and unafraid to challenge vested interests. This week it will be bold again, pushing for the UK to become the first country in the world to recognise that we are facing a climate emergency. Once accepted, this is a truth from which there can be no reversing. No half measures will be possible and the consequences for public policy-making and how we live will be – should be – significant.

So, to Europe. Three years after the Brexit vote, there is no easy way out of the near cul de sac into which an inept Tory government and a fractured parliament have driven us. The divides in our country will not fade if we simply wish them away or be tidily stitched up by a “deal on a customs union”. We will have to work hard to repair Britain, community by community.

The challenge we face in the forthcoming European elections is not whether Labour should back a “confirmatory vote” or a “public vote on a Tory deal”, or any of the other variations on these themes circulating in Westminster’s WhatsApp world. The real challenges we face are those described by the phenomenal Greta Thunberg – and the rise of the far right.

Nigel Farage – who in 2016 stood in front of the infamous “breaking point” posters, whipping up hate against immigrants – is now on tour, vaunting his aim to “put the fear of God” into politicians and stoking anger about the “betrayal of the people”. This is populism unplugged. There is no manifesto to argue about, there will not be one. Just the simple offer of “Brexit” – which the past three years have taught us is anything but simple.

And Farage is just the rightwing warm-up act. Stephen Yaxley-Lennon – stage name Tommy Robinson – a far-right racist thug, is standing to be an MEP too.

Across Europe, Farage and Robinson are united with others in an online world of untruths and hate. From viral videos of fascists with swastikas to an endless stream of propaganda from Matteo Salvini, whose League party is now at a worrying 32% in the national polls (my Italian family and friends are confronted with the same).

My husband’s home town Dogliani is in the only region in northern Italy still run not by the Lega but by the Partito Democratico. The PD is hoping for renewal after primaries in which some 1.8 million people turned out to elect a new leader, motivated by the memory and fear of populism and fascism. The parents and grandparents of Dogliani’s PD remember fascism. As its dark colours seep again across the Italian map, they know they must do what they can to halt it.

To take on Salvini, the PD activists know that a rupture with the politics of refusing-to-take-a-side is needed. Because there is only one side when it comes to the question of why ordinary voters pay more in taxes than global corporations. There is only one side when it comes to the defence of migrants’ rights, wherever they are and wherever they are from. There is only one side if we are to save our one planet.

For the PD, the Labour party under Corbyn offers enormous hope because it has decided to take a side.

Labour must take a side again now. We must fight these European elections with a positive vision, with honesty about the challenges we face, determination to run at and not away from them, and clarity about where we want to go. The party should continue across Europe the campaign it has begun in the UK: ending the age of European austerity, promoting public investment, tackling international tax cheats and returning wealth to those workers who have created it. There is more than enough for the many if we take on the few.

In doing this we will deprive Farage, Robinson, Salvini – and their friends Marine Le Pen in France and Viktor Orbán in Hungary – of the oxygen of inequality that feeds the flames of despair and hate. Energy spent fighting fascists can be converted into the energy needed to take on the epic task of meeting Greta’s challenge.

Labour’s members already know which side they are on. The party should commit to bringing whatever Brexit deal is done back to the people, for our final say – and then to lead and win the argument for remaining in, and transforming, the EU.

• Laura Parker is standing as a Labour candidate for the EU elections.