Garvan Walshe is a former National and International Security Policy Adviser to the Conservative Party. He runs Brexit Analytics.

Here in Budapest, attention last Sunday was not focused on Jeremy Corbyn’s appearance on the Andrew Marr show. The previous’ day’s pro-democracy demonstrations, following Viktor Orban’s artificial electoral landslide, captured attention in a region whose leaders are experimenting with self-described “illiberal” governance.

Fellow illiberal democrats in Warsaw will watch his handling of the fractured opposition closely. To the over 100,000 people packed into Lajos Kossuth square in front of the gothic revival parliament calling him “Viktor Orban, Diktator”, he will surely reply that the fact they are able to do so shows that he isn’t one.

It is external aggression, not internal upheaval, that should worry the Polish government. The ruling Law and Justice Party counts the UK as its closest European ally. It had thought it found a kindred spirit in a Britain where major newspapers brand Supreme Court judges ‘Enemies of the People’, and the Prime Minister’s former chief of staff (and former fellow columnist here) puts his name to long articles accusing George Soros of subverting democracy.

Indeed, the alliance has long been deeper. Before Brexit, the UK weighed in to support to efforts to contain Russian expansionism and subversion, and since the referendum has reinforced its commitment to European security by leading the NATO’s Joint Forward Presence in Estonia. In British security and defence circles, officials have with good reason been every bit as exercised by Russia’s so-called “hybrid war” as they are in Poland.

Sunday’s intervention by Jeremy Corbyn should be taken as a signal that it could be coming to an end. As Ed Miliband did over Syria, he exploits a false analogy with Iraq to justify his opposition to air strikes.

Where the Iraq war was an ambitious project of regime change, these strikes had the very limited ambition of deterring future uses of chemical weapons by the assad regime.

Where the Iraq war divided the world’s major democracies, France joined in these strikes and Germany offered them strong diplomatic support.

Where the Iraq war began without UN weapons inspectors locating WMD there, the UN’s Organisation for the Prohibition of Chemical Weapons this time confirmed the gas had been used to murder civilians in Douma.

The real difference, however, is more fundamental. Opponents of the Iraq war argued that it constituted a violation of the norms of international order. They said it was an unprovoked invasion of a sovereign state that posed no threat to its neighbours and was not engaged in systematic violence against its own people. Both those claims were contested by the war’s supporters, but there was agreement about the need to support international norms.

Corbyn did not dispute there is a norm against the use of chemical weapons; what he objected to was any means of enforcing it that wasn’t endorsed by the UN Security Council. This amounts handing Vladimir Putin a veto over all coercive enforcement of international law.

By doing so, he subverts two principles of international society: the right to self-defence, and the responsibility outsiders have to protect civilians who are being killed by their own governments. The Security Council has the right (indeed, the duty) to intervene to regulate the international use of force, and its decisions are binding in international law on all members of the UN: but its role is not to be a procedural hurdle to be crossed. The Council isn’t like the US Senate, which must give its permission for war. It is there, rather, to prevent military action by individual states when it achieves consensus about how to do so.

Its members, and most obviously its permanent members, are supposed to operate under a duty to uphold international peace and security. They can’t outsource decisions about peace and war to the Council, because they are themselves part of it. To do so is to abdicate the responsibility that goes with the office, not to respect it.

Corbyn’s problem here, as with in enforcing the norm against anti-semitism, is that he doesn’t understand the responsibilities of office, whether as leader of one of the country’s main political parties, or as the potential leader of a Permanent Security Council state. He thinks he can avoid judging anti-semitism in his party, and enforcing international norms at the UN, by passing decisions on to others.

Make no mistake, should be become Prime Minister the same pattern of evasion will continue. Corbyn’s Britain will be powerless to deter Russian aggression, because he doesn’t see upholding peace and security in Europe – let alone the world – to be part of his job.

Optimists hope that the Labour Party, which has traditionally been pro-NATO and suspicious of Moscow, would goad him into action if necessary. Their hopes are probably misplaced: Labour is even more pro-European than it is pro-defence, and they haven’t got him to oppose Brexit.

While Germany’s decision to see Russia’s Nordstream 2 pipeline as political was good news for Eastern Europe, Corbyn’s “neo-neutralism” will offset that benefit. East-Europeans in particular need to look beyond Brexit, to the geopolitical revolution a Prime Minister Corbyn would bring.