Four examples of Prime Ministerial power – how Boris Johnson in fact ‘did everything he could’ for there to be a trade barrier down the Irish Sea

4th February 2021

You will no doubt have an opinion on Boris Johnson, the current prime minister of the United Kingdom.

For my part, the best and most insightful depictions of Johnson as a politician are this piece by Marina Hyde and this by Rafael Behr.

This post, however, will look at the prime minister not just as politician but also through the lens of constitutional law and practice – and, in particular, will examine one statement he made yesterday.

Everyone who cares knows that Johnson will not do – and has not done – ‘everything’ to avoid a barrier down the Irish Sea.

The fact that this statement is untrue is by itself neither here nor there: more than most politicians, Johnson knowingly says false things.

But for this blog, what is interesting about this lie is that its falsity engages four distinct examples of prime ministerial power.

For Johnson did everything as a prime minister for there to be a barrier down the Irish Sea.


Within a parliamentary system such as the United Kingdom, and with the constitutional theory that executive power flows from the crown, there are limits to what any prime minister can and cannot do.

But the Irish barrier question shows the ways in which a prime minister can exercise power.


First, a prime minister can change and set government policy.

And here Johnson broke with the policy of his predecessor on the (once infamous) ‘backstop’ in the withdrawal agreement.

Johnson, of course, did this for cynical reasons of political convenience – but it is a decision that only a prime minister could have made.

And Johnson did.


Second, a prime minister can enter into international agreements.

In constitutional theory, this is the prime minster using the royal prerogative to enter into those international agreements.

So having reversed the policy of his predecessor, he proceeded to agree the withdrawal agreement providing for a trade barrier down the Irish Sea.

And again, this was something he could only have done as prime minister.


Third, a prime minister – as leader of the party that wins a general election – can win a mandate for their policies.

Currently, calling a general election is outside the powers of a prime minister, by reason of the Fixed-term Parliaments Act.

But when there is a general election, and that election is won, the prime minister (and the winning party) then enjoys a mandate for their manifesto commitments.

And this mandate is constitutionally significant – for example: any policy with such a mandate cannot be blocked or delayed by the house of lords.

The (then) ‘oven-ready’ deal was mandated by the 2019 general election.

So, again, a mandate was something Johnson achieved as a prime minister (and which his predecessor failed to do with the 2017 general election).


And fourth, a prime minister is ultimately responsible for the government’s programme of legislation.

So: having reversed policy, entered into an agreement with the European Union giving effect to that new policy, and having won a mandate for the policy in a general election…

…the prime minister now ensured that the policy was implemented into domestic law with an act of parliament.

(Legislation that, of course, was pushed through with minimal scrutiny using the government’s newly obtained overall majority so as to ‘Get Brexit Done’).


That there is now a trade barrier in the Irish Sea is a perfect illustration of the various powers of a prime minister under our constitutional arrangements.

The trade barrier in the Irish Sea was Boris Johnson’s policy (which he reversed from his predecessor), which he agreed with the European Union and for which won a mandate in a general election, and that he then ensured was enacted into domestic law.

There was nothing more Johnson as prime minister could have done for there to be this trade barrier in the Irish Sea.


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11 thoughts on “Four examples of Prime Ministerial power – how Boris Johnson in fact ‘did everything he could’ for there to be a trade barrier down the Irish Sea”

  1. Mr Johnson has a very poor opinion of the intellect of the average British voter (he may not be misguided, alas (!)). For most people, the act of lying about something is an attempt to decieve a specific person or group of people. Few people continue to lie when confronted with irrefutable proof of the truth; not so Mr Johnson.

    Johnson uses lying as a “temporal” deflection technique to buy time that can put off some evil day for a while. He is aided and abbeted in this by sections of the press and his own party (like you, David, I know what he said: how difficult would it have been for a “professional” Sky journalist to confront him with his own words and actions?).

    I hope that the American political flirtation with “fake news” has ended (I hope…), but in this country, perhaps, we have power in our own hands to call this out, as indeed you have. I think it is our responsibility to do so. In an age not so long gone, Johnson would have been forced out of public life to shame and ruin for what he has done, the lies he tells and his own lack of morality. In our time, he will eventually slink off the public stage, but only to make millions in private life. We need to add fixing the morality of public figures to our “to do” list of restoring true democracy to the land.

  2. All of Johnson’s actions on the island of Ireland are almost the equivalent of Sir Anthony Eden thinking that the Suez Canal was part of the British Empire and that France and Israel could just walk in and stop the Egyptian government from nationalising a company operating within their country. That Eisenhower stepped in may prompt his successor Biden seeing the parallel and the dangers inherent in this very British exceptionalist approach to trade and world politics.

  3. “Comments are welcome, but they are pre-moderated.

    Comments will not be published if irksome.”

    Out of interest David, what proportion of comments do you have to weed out for being ‘irksome’?

    It would be particularly interesting to know whether, at the end of the day, this piece (whose profile may be raised following its endorsement by David Gauke) has generated a higher than usual proportion of such vexatious comments?

      1. Watch this space. I predict that after this piece, the bemused Russian pornbots may be replaced by enraged Russian leavebots.

      2. I find that astonishing (and refreshing), considering how unpleasant most online comment spaces seem to be, and the extremely contested nature of Brexit, a common theme here. Maybe the fair-but-firm sign over your blog door is having some effect.

  4. Dear David – many thanks … again!

    I think what you highlighted is perhaps best known as ‘Dani Rodrik’s trilemma’. In summary, nations can only have 2 out of 3 options – national independence, democracy and integration with globalisation. They can’t have all 3. In the context of Ireland, the former British ambassador to Brussels, Ivan Rogers, was fully aware of another issue closer to home, namely the ‘Irish’ trilemma facing Britain – he said that much to Theresa May when prime Minister and Boris Johnson when foreign secretary. His comments were that three contradictory commitments were made to differing audiences depending on who the audience was. The Irish were told that there would be no hard border across the island of Ireland; the Democratic Unionist Party was told that there would be no divergence from Great Britain; and the Conservative Party was reassured that the UK was leaving the single market and the customs Union: ‘You’ve got to choose two of the three.’

  5. Arlene Foster needs to read this blogpost. She’s quoted in the article below as saying: “UK government ‘sleepwalked’ into protocol plan”

    But as David’s post demonstrates beyond doubt, Boris Johnson had his eyes wide open about the consequences of what he negotiated, sought a mandate for, and then put into law.

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