In an interview with Channel Four News on 1 February, Zack Polanski wobbled. Questioned about his party’s position on Nato, the leader of the Green Party gave two answers. He said he thought the alliance could be reformed from within, then appeared to backtrack. “What I am arguing for is an alternative alliance with countries based in Europe, plus Brazil and Mexico and global south countries,” he said, “I don’t think it’s possible to reform Nato from within.” Prodded on the apparent contradiction in his answers, Polanski insisted “I think we can do more than one thing at once.” But can he? 

The Greens have seen unprecedented success since Polanski was elected leader in September 2025. The party won last month’s by-election in Gorton and Denton. A recent poll put the party second only to Reform, with 21 per cent, overtaking both Labour and the Conservatives. But success attracts scrutiny. Polanski has been challenged on his economic policy and his party’s tolerant approach to legalising drugs. But the most salient difficulty to emerge so far concerns the party’s approach to defence.

Defence in general, and Nato in particular, has long been a vexed question for the Greens. The party’s position has shifted and evolved over the past few years. Until the outbreak of the Ukraine war in 2022, party policy was to withdraw from the alliance. After the war it modified its stance to supporting withdrawal only once the war was over. Adrian Ramsay, then party leader, told Sky News that withdrawal remained the “long-term policy”. But at the party’s 2023 spring conference, members voted to ditch withdrawal and seek instead to reform the alliance from within. 

Before he was elected leader, Polanski said he would return the Greens to a pro-withdrawal position. When I interviewed him in May 2025, shortly after he had announced his intention to run to become Green Party leader he said of the idea that Nato was failing: “I don’t think it’s contentious.” 

At present, the Green Party’s position remains advocating for reform from within. A spokesperson told me: “Our party policy – decided by members – supports the principle of international solidarity, recognises the role of Nato in ensuring the ability of its member states to respond to threats to their security, and sets out a number of amendments Greens would pursue to reform Nato from within.”

After his election – and once the Green Party began gaining popularity – Polanski kept to the party line, and to speak about reforming rather than quitting Nato. At the World Transformed in October 2025 Your Party co-founder Zarah Sultana aimed to outflank Polanski on his left, arguing that the Green Party’s official policy of reform was not a “socialist” position. “I’m sorry, you cannot greenwash Nato, the socialist position is that we must leave Nato immediately,” she said. 

If he wished, Polanski could put the question to a members’ vote. But will he? A source close to Polanski said the Greens are aware that conversations around defence can make people “nervous”. The Green Party leader had planned to use the start of the year to sit down with his team and work out a coherent policy platform, but had his brainstorming delayed by the Gorton and Denton by-election. 

Galvanised by his party’s victory, however, Polanski is now trying again. He has been speaking to thinkers from left-wing think tanks such as Common Wealth and the New Economics Foundation to develop a clearer position on defence and other key policy areas such as the economy, and tackling the cost of living crisis. Regarding defence, the Green Party leader instead plans to spend the next few weeks exploring how Nato might operate differently and further domestic British interests, rather than as a tool to exert British influence abroad. 

Khem Rogaly, co-director of the Transition Security Project, which is run out of the progressive Common Wealth think tank. According to sources close to Polanski, the Green leader and Rogaly have spoken informally about how Polanski might shape his defence policy. Rogaly told me that Polanski is “looking to understand what security means in terms of the safety of citizens, rather than meeting US demands”.  He added: “This means highlighting that the UK’s strategy includes outdated priorities like global power projection and an archipelago of bases, designed for use by the US.”  

Rogaly also suggested a potential attack line for the Greens. The party, he argued, could push the government for more accountability on what increases in defence spending are actually for. The Ministry of Defence is already castigated regularly by the National Audit Office for wasteful procurement processes. “Decisions like accepting the new Nato target which could shape the UK’s fiscal outlook for decades – requiring more than £100 billion per year in additional spending from 2035 – are made without explaining what the money will be used for,” he said.

But for some long-time members of the Green Party, the Polanski-led leftwards shift on issues like defence has been off-putting. Darren Johnson, a former London Assembly Member for the party and its London Mayoral candidate between 2000-2004, who left the party in 2024 after being suspended for criticising the party’s response to the Cass Review, said Polanski’s position on Nato “sends out so many wrong signals at a time like this”. He added: “We all understand problems around Trump but to try and trash Nato at this stage just seems wholly irresponsible”. After the Gorton and Denton by-election, Johnson joined the Labour Party. 

Defence policy has historically been a vulnerability for leaders on the left. Shortly after Jeremy Corbyn was elected leader of the Labour Party in 2015, an anonymous “senior serving general” warned of a “mutiny” among military personnel if he ever became prime minister. The idea of Corbyn being a threat to national security trailed him throughout his career as Labour leader.  As he has so far articulated it, Zack Polanski’s position on Nato is reminiscent of Corbyn’s. 

Polanski appears to have been caught between his own personal views about Nato (that the UK should withdraw in favour of a new defensive alliance) and the position adopted by his party in 2023. One is more palatable to the British electorate than the other: the UK would flounder outside of Nato, as our defensive capabilities are inextricably linked to this 77-year-old alliance. Reform from within, if articulated correctly, is likely the more favourable option if Polanski really is serious about “overtaking Labour”. (There is at least one senior Green politician who remains against the party advocating for withdrawal from Nato). 

But the Greens also know that the new geopolitical landscape also poses an opportunity. Donald Trump’s second presidency has forced a reckoning for the UK and its European allies as doubts grow over whether the United States will remain a dependable guarantor of Nato’s collective defence. Just 36 per cent of Britons think that the “special relationship” even exists. Keir Starmer is struggling to balance keeping the US on side while also standing up for British interests. Polanski and his allies understand he has a chance to pressure the government from the left and to offer a progressive alternative. As Rogaly said, “without allowing for democratic debate over this strategy, politicians cannot claim to be invested in keeping the country safe.”

[Further reading: Oil prices mean Starmer must raise tax or face recession]

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