Any sovereign state has the power to resile from its international treaty commitments. Whether it is right or wise to do so is an entirely different question.

International law matters. The Nuclear Non-Proliferation Treaty and the international bans on chemical and biological weapons are vital to our security. Theresa May and Boris Johnson rallied global support after the Salisbury poisonings on the grounds that Russia had breached the Chemical Weapons Convention. The right of the United Kingdom and other independent coastal states to an exclusive economic zone derives from international law. British Ministers in this and previous governments have cited international legal obligations to press other countries to respect freedom of speech, worship and political expression.

It is through treaties, binding on their signatories, that we are able to secure favourable terms for our exports, extradite suspected criminals from other jurisdictions, transfer prisoners to serve their sentence in their home country, stop the trade in products from endangered species and ensure global action on the environment. The United Kingdom’s security, prosperity and influence benefit from the rule of law between nations. Upholding international law is both a moral duty and in our own national interest.

Successive British governments have also recognised that treaties need to include specific measures that encourage implementation. Margaret Thatcher, speaking to the United Nations in 1989, hailed the success of earlier treaties in obliging nations to take action to curb ozone depletion and called for a new international convention on climate change. She was explicit that a framework, what she termed a “good conduct guide for nations”, would not be enough. In her words: “It will need to be filled out with specific undertakings or protocols in diplomatic language… These protocols must be binding and there must be effective regimes to supervise and monitor their application”.

Ministers in the present government, like their predecessors, call out leaders like Putin, Assad and Xi for breaching treaties which their countries have signed. A United Kingdom that starts to pick and choose which treaties it observes will be in a weaker position to hold others to account. As my old boss Michael Howard put it the other day, “How can we reproach Russia or China or Iran when their conduct falls below internationally accepted standards, when we are showing such scant regard for our treaty obligations?”

The baffling feature of the government’s position now is that it seems willing to take the existential step of deliberately overriding international law, with the harm to our reputation and our interests that that involves, because of concerns about details over the content or the interpretation of its own Northern Ireland protocol that could be dealt with in other, less belligerent ways.

The protocol negotiated by the present government requires Northern Ireland, but not the rest of the UK, to follow the EU customs code and also EU single market rules relevant to North-South trade on the island of Ireland. Checks and administrative procedures between Great Britain and Northern Ireland will ensure that those rules are being followed. Indeed that was why the Democratic Unionist Party objected strongly to the new deal.

The protocol provides for these arrangements to apply with or without a UK/EU trade deal but also gives the Northern Ireland Assembly the right to cancel them.

The government’s concerns appear to centre on three objectives: to get the EU to waive its normal customs code requirements to allow Northern Ireland to Great Britain trade without the need for online exit declarations; to ensure that the application of EU rules on state aid to Northern Ireland do not give the EU power automatically to vet state aid to any Great Britain company that has a Northern Ireland outpost or subsidiary, and to have certainty that the checks and tariffs required on food shipped from Great Britain to Northern Ireland do not make it uneconomic for the producers to supply Northern Ireland’s shops and supermarkets.

All three are pragmatic, reasonable demands. And they ought to be addressed either in the main UK/EU trade negotiations or in the Joint Committee established under the Protocol to thrash out details on how the deal should operate in practice. The government’s Withdrawal Agreement also establishes a dispute resolution and independent arbitration procedure to resolve any differences over how the Treaty and Protocol should be interpreted while Article 16 of the Protocol includes the power for either side to take unilateral safeguarding action in the event of “serious economic, societal or environmental difficulties…or diversion of trade” – a provision that would surely cover the disruption of food supplies to Northern Ireland.

Given the existence of these alternative mechanisms, for the government to seek its objectives by setting aside a binding treaty – a treaty furthermore that this government itself negotiated, agreed and embodied in legislation less than a year ago – seems a wholly disproportionate response. I hope, even at this late stage, that ministers will think again.

Next year, the Prime Minister will carry forward Margaret Thatcher’s vision when he hosts a UN global summit on climate change in Glasgow. It will be an unequalled opportunity for global Britain to show how, post-Brexit, it can still exercise leadership and influence in international affairs. And it is not an exaggeration to say that the whole of humanity needs that summit to be a success. Part of what the Prime Minister and his team will want to do is persuade other world leaders to deliver on their treaty commitments to reduce carbon emissions. Our voice will be stronger and more persuasive if we ourselves have stuck to our longstanding tradition of upholding the rule of international law.

Sir David Lidington served as Minister for the Cabinet Office and Chancellor of the Duchy of Lancaster from 2018-2019. He is a former Europe Minister.