IN his daily address on Monday, President Zelenskyy announced his concern – one previously voiced by the United Kingdom and United States – that the Russian occupying forces could use chemical weapons against the Ukrainian defenders in Mariupol.

These weapons – any kind of “asphyxiating, poisonous or other gases” – have been banned since the signing of the Geneva Protocol in 1925. Their use in international conflict has been illegal for almost a century. The UK Foreign Secretary stated on Monday that “any use of such weapons would be a callous escalation in this conflict and we will hold Putin and his regime to account”.

This is a story we have heard before. In 2013, the Syrian regime – with political and diplomatic cover provided by the Russian government – used the nerve agent sarin against its own citizens, killing nearly 1400 people, including more than 400 children. The West was united: then US vice-president Joe Biden echoed the UK and France in stating that there was “no doubt” that Syrian president Bashar al-Assad was responsible for this atrocity and vowed that he “must be held accountable”.

With international reluctance to pursue a military solution, the UK, France and the US – the three powers who had vowed to hold Assad to account – chose to pursue a diplomatic path. In late 2013, the US and Russia signed an agreement in Geneva to dismantle Syria’s chemical weapons capability, while forcing the Assad regime to join the international Organisation for the Prohibition of Chemical Weapons (OPCW).

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The following year, in 2014, a joint UN and OPCW report found that Syrian military helicopters had dropped chlorine gas in Idlib, a rebel-held province. The next year they did the same. And the next year they did the same, too.

Undoubtedly, the international coalition failed in their promise to hold Assad accountable for the use of chemical weapons and deter their future use by other actors.

And so we find ourselves, years later, hearing echoes of the same warnings given in Syria. President Biden has warned that Russia would pay “a severe price” for any chemical weapons attack. Likewise, the secretary-general of Nato has stated “there will be a high price to pay” if Putin uses chemical weapons in Ukraine.

Having failed to provide meaningful deterrence against the use of these weapons in Syria and, indeed, in Salisbury, these words must now be backed up with concrete action.

However, as the White House press secretary stated last month, the West has to weigh “how you can make very clear that actions are horrific, that they are not acceptable, they’re not aligned with global norms, while also thinking about our own national security interests. And starting World War Three is certainly not in our national security interests”.

It is a difficult line to walk. But the rules-based order means nothing if no one is willing to defend it. It means nothing if there are no meaningful costs to breaking its laws. If we agree that an enforceable system of international norms is the best way to ensure our continued peace and prosperity – as they largely have done since the end of the Second World War – then we must be willing to defend and strengthen that system.

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Ukraine serves as a deadly lesson of just what can happen when the rules, laws and norms that govern the international system are left to wither on the vine. The horrors we are witnessing in Ukraine show what happens when global leaders can break international law with little or no meaningful consequences.

This call rings true at home as well as abroad. Just last month, the Prime Minister described Saudi Arabia – a state which orchestrated the murder of a journalist and the dismemberment of his corpse – as a “key international partner”. The same Prime Minister has presided over a government which has made its contempt for domestic and international law clear, demonstrating its belief – whether through partygate or the Chancellor’s creative tax arrangements – that the rules are for the little people.

This situation is untenable. While enforcing and strengthening international law, as the White House press spokesperson pointed out, is often complex and difficult, there is no such excuse at home.

If the UK Government is now waking up to the importance of shoring up the rules-based order rather than playing its part in its gradual erosion, I cannot but welcome that. This age of impunity must end – at home and abroad.