COMMENT: Friends don't let friends drive drunk, as the saying goes, and for similar reasons we call on our respective governments to weigh in officially on Brexit.
In the post-1945 era, New Zealand and Canadian governments have generally subscribed to the UN doctrine of non-interference in the internal affairs of sovereign states. But exceptions should be made. We believe such a moment has arrived two years after the UK voted narrowly to leave the EU in a fiercely contested referendum.
Historically, Britain, New Zealand and Canada have shared a commitment to a rules-based international order that is enshrined in institutions such as the UN and norms such as multilateralism and free trade. But these interests and values are being challenged by the refusal of Theresa May's government to recognise that its Brexit policy has a legitimacy deficit.
For many observers outside the UK, with some exceptions like Donald Trump and Vladimir Putin, it was always a stretch to claim a 3.8 per cent margin of victory for the Leave camp in a non-binding referendum was sufficient justification for the greatest change in Britain's external policy since World War II.
And little has happened since the referendum to boost such claims. Having called for a clear Brexit mandate at 2017's General Election, May's Conservative Party saw its majority slashed and had to form a minority government with the support of the Democratic Ulster Party.
At the same time, the May Government has over two years failed to develop a workable plan to withdraw from the EU that would avoid economic disaster.
According to projections by the UK Government's own Department for Exiting the European Union and the Office of National Statistics, an increasingly likely "hard" Brexit would lower the UK GDP by 8 per cent or £158 billion ($304.6b) and cost 2.8 million jobs. Even a "soft" Brexit that kept Britain in the Single Market, with no say in EU decisions - would lower the GDP by 2 per cent (£15b) and put 700,000 out of work.
This is to say nothing of the intractable problem of the Irish frontier. Anything akin to the status quo would effectively separate Northern Ireland from Britain; any significant barrier would risk triggering renewed sectarian violence.
Yet the May leadership and Brexit backers insist the "British people have voted to leave the EU" and reject calls for a second referendum on EU membership.
In addition, we now know the integrity of the EU referendum result was tainted.
In May 2018, Leave.EU, one of the main Brexit campaign organisations, was fined £70,000 by the UK Electoral Commission for exceeding its legal spending limit by at least 10 per cent and furnishing incomplete and inaccurate documentation. Vote Leave, a campaign group headed by Boris Johnson and Cabinet member Michael Gove, has been fined £61,000 by the UK Electoral Commission and referred to the police for serious breaches of electoral law.
Furthermore, the UK's Information Commissioner's Office fined Facebook £500,000, the maximum possible, for allowing improper use of millions of users' data by Cambridge Analytica and is pursuing a criminal prosecution of its parent company, SCL Elections, linked to a Canadian business that provided analysis for the Vote Leave campaign.
Finally, there is growing evidence Putin's Russia colluded with the Brexit camp to influence the outcome of the 2016 referendum.
Yet the May Government seems determined to "reclaim" British sovereignty even if it is on the back of breaking British laws.
It is time for old allies like New Zealand and Canada to firmly remind London that in a democracy the integrity and trust of the voting public is dependent on governments upholding the rule of law, and that failure to do so not only diminishes the UK but weakens the fabric of the liberal democratic order at a time when it is threatened by the likes of Russia.
• Professor Robert Patman teaches international politics at the University of Otago. Professor David Welch teaches global governance at the University of Waterloo.