US presidential candidate Joe Biden’s intervention last week on the UK’s increasingly bizarre and dangerous-looking Brexit odyssey highlighted the gulf between the big promises of Boris Johnson’s Government and reality.

The Democratic candidate took to Twitter last Wednesday to declare: “We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit. Any trade deal between the US and UK must be contingent upon respect for the Agreement and preventing the return of a hard border. Period.”

His intervention came after the Conservative Government’s controversial internal market bill cleared its first hurdle in the House of Commons on Monday last week, in spite of concerns over a breach of international law in the context of the withdrawal agreement signed by the UK and EU in January.

The UK Government’s decision to bring forward legislation which could override key aspects of the existing withdrawal agreement with the EU relating to Northern Ireland has of course caused widespread concern at home and among our long-suffering European Union neighbours.

READ MORE: Opinion: Ian McConnell: Moderate Tory voices absent as UK Brexit crusade at full tilt

Mr Biden’s intervention came hard on the heels of Democratic House of Representatives Speaker Nancy Pelosi’s warning the previous week that any move by the UK to erect a physical customs border between Northern Ireland and EU member Ireland meant “absolutely no chance” for a US-UK trade deal.

She said: “If the UK violates that international treaty and Brexit undermines the Good Friday accord, there will be absolutely no chance of a US-UK trade agreement passing the Congress. The Good Friday Agreement is treasured by the American people.”

Both of these interventions are stark reminders of the wider global ramifications of Mr Johnson’s move to go back on a key, and politically charged, aspect of his Government’s previous agreement with the EU. And that is even before we get to the longer-term reputational damage to the UK of such behaviour.

Paul Sheerin, chief executive of industry body Scottish Engineering, wrote in The Herald on Monday: “As someone whose working purpose is to represent the best interests of Scotland’s engineering manufacturing sector, thankfully the wider implications of this move in areas such as the Good Friday Agreement and the UK’s devolved administrations I can leave for others to chew over. However, the further erosion of trust and goodwill with the UK’s largest trading partner – 43% of exports in 2019 – resulting from this [internal market] bill is something I am happy to wade in on, as I am yet to find anyone in my industry willing to defend an action that tears up a legally binding agreement signed and celebrated by the same Government just months before.”

He added: “Even in the event that such strategy delivers an agreement, we should consider at what cost if it’s achieved through the use of such a threat. Who would want to do business with a UK that behaves in such a way? Inwardly invested businesses (owned outside of the UK) in Scotland represent a very small proportion of our companies and a much larger proportion of our employment and gross value-added. Some are headquartered in Europe and some will have choices where to base their high-value operations providing quality skilled employment.”

READ MORE: Opinion: Ian McConnell: Rock-bottom hopes of sense on Brexit but Tories still disappoint

We are a very long way indeed from Mr Johnson’s promise last autumn of an “oven-ready” Brexit deal.

It is perhaps just as well, in terms of the time it is taking the Tory kitchen to prepare this order, that Mr Johnson is not a restaurant owner.

Sadly though, this is a far more serious matter than a tardy kitchen with some perplexed diners.

It is a shambles of epic proportions, one that was entirely unnecessary and has arisen from the grim ideology of Brexit, with all its insularity and anti-immigration rhetoric.

Remember the jubilant Brexiters’ declamations, after they “won” the 2016 vote, about the big new trade deals the UK would now be free to go on to secure? Completely ignoring the fact that they were, with their determination to leave the single market, giving up much larger benefits in terms of truly frictionless trade with the UK’s biggest trading partner and the economic advantages of free movement of people and immigration flows.

Of course, the Brexiters’ promises have come to nought, with the UK having failed spectacularly to move towards anything meaningful in terms of trade deals that it would not have had as part of the EU. Much-vaunted progress with Japan is around a deal that largely replicates the existing agreement between the East Asian country and the EU.

The Tory vision of a welter of big new trade deals the UK could not have had as part of the EU looks in any case to be a pipe dream, and any future prospects might be hampered if countries look at the Conservative Government’s attitude to the EU withdrawal agreement.

Mr Biden’s comments last week, and Ms Pelosi’s remarks earlier this month, obviously highlight potentially major problems for a UK-US trade deal.

The UK has been engaged in several rounds of talks on a free trade agreement with the US. The signs are that, in spite of an outpouring of enthusiasm from the UK side about the US that has been in stark contrast to an at-best-tetchy attitude to the EU, significant stumbling blocks remain in efforts to negotiate an agreement.

And that is before we get to the US presidential election in November.

READ MORE: Opinion: Ian McConnell: If this is not time-wasting, just what is the Tory Brexit game?

Mr Biden has made his view on Brexit and Northern Ireland clear. And, regardless of the outcome of his battle with Donald Trump, the House of Representatives is expected to remain in Democratic hands after the November elections. A trade deal on the scale being negotiated between the US and UK, if it ever comes to fruition, is expected to require the approval of Congress. So Mr Johnson and his Brexit-minded Cabinet would do well to reflect on Ms Pelosi’s “absolutely no chance” remarks.

Even if a US trade deal were to be finalised, the economic benefits of such an agreement, based on the very calculations of the Johnson Government, would be chicken feed relative to what the UK stands to lose from the Tories’ incomprehensible drive to irritate our EU neighbours.

And we also need to keep in mind that a Brexit which clamps down on immigration from European Economic Area countries will cause major damage to the UK economy over years and decades even if the Johnson Government is yet able to secure an average free trade agreement with the EU.

The Conservative Government has noted in its own paper on its sought-after trade deal with the US that such an agreement could, in the longer term, boost UK gross domestic product by around 0.07% or 0.16% under two different scenarios.

The Theresa May government forecasts, published in November 2018, show, even if there were no change to migration arrangements with Brexit, UK GDP in 15 years’ time under a no-deal scenario would be 7.7% lower than if we had stayed in the EU.

We now know beyond doubt, of course, that the Conservatives plan to clamp down on immigration dramatically, and have pushed ahead with legislation to enable that.

On the basis there is zero net inflow of workers to the UK from EEA countries, the forecasts from Mrs May’s government have it that GDP in 15 years’ time would in a no-deal exit be around 9.3% lower than in a scenario in which the UK had remained in the EU. If the UK were to conclude an average free trade agreement with the EU, the hit to GDP would be 6.7% on the scenario of zero net inflow of EEA workers, according to the forecasts.

All in all, it looks to be one problem after another for Mr Johnson. It is almost as if his Government’s solution is to become noisier as the troubles mount. Sadly, such tub-thumping looks highly counter-productive.

Brexit is proving to be a real Pandora’s box for the Leavers, taking at face value a euphoric attitude from them which has suggested they did not foresee the problems many millions of others did.

The Johnson Government had the chance to shut the lid of the box by putting off the grim day when the transition period ends and the UK leaves the European single market. However, it refused to agree an extension of the December 31 end-date by the deadline of July 1.

The EU was willing to agree an extension, but the UK set itself against so doing, even as the huge economic fall-out from the human tragedy that is the coronavirus pandemic became ever clearer.

The Pandora’s box of Greek mythology is today used to describe “any source of great and unexpected troubles” or, alternatively, “a present which seems valuable but which in reality is a curse”.

The troubles are great, although unexpected largely to Brexiters it seems, with Remainers never in any doubt over the Leave folly.

Having said that, it may be that the Leavers, including those in Mr Johnson’s Cabinet, will refuse to acknowledge the “great and unexpected troubles” even as these develop around them, with the seeming disregard for the fury caused by the internal market bill just the latest example of a head-in-the-sand approach.

Meanwhile, the first element of the latter version applies only to the Brexiters – nearly half of the population in the UK and a big majority in Scotland never saw the right-wing Tory “present” of Brexit as “valuable”. That Brexit is in reality a curse is a plain and simple fact, already proved by subsequent events, even before we get to the real woe.