IN modern diplomacy there is probably more nonsense spoken about the “special relationship” between the United States and the UK than any other bilateral arrangement. It is a glib phrase used by politicians on both sides of the Atlantic to play to their publics, far more commonly here than in the US. In all truth, if the special relationship exists, and that is a debatable proposition, it is only within the realm of national interest.

The US and the UK have cooperated often and closely over the past 80 years not because they like each other more than other countries; it is because their political leaderships have concluded that their national interests, for selfish reasons, made it prudent that they do so. Sentiment is meaningless in the process.

This brings up the question of how any Trump administration will deal with the UK in the coming years. Assuming that Donald Trump’s team is not entirely irrational, and approaches the question from the point of view of US self-interest, it could be a very difficult time for Britain. There is a delusion amongst the Brexit-supporting press that the Trump administration, partly because of its love for Nigel Farage, will somehow promptly cut a favourable trade deal with the UK.

This has been trumpeted a number of times by those who have argued that Brexit will free the UK to make itself attractive to the world. Mr Trump said over the weekend that he wants a trade agreement between the two countries secured quickly.

The truth is dawning, however, that Brexit will give the US an extraordinary upper hand in negotiations with the UK. The UK will be desperate to conclude such a deal as soon as possible, while it will be a low priority for the US. The reason is a combination of economic imbalance and political need. Economically, US-UK trade is a very big part of British commerce but it takes up a relatively small part of American output. The US takes more British exports by value than any other country in the world, though this figure is dwarfed by the amount the UK sends to the EU as a whole. On the other hand, what the US imports from the UK is a very small percentage of its trade. In other words, Britain will desperately need to trade with the US in any Brexit world; the US, not so much.

Moreover, the US can do many of the things Britain specialises in but has been able to develop within the EU. This is particularly the case in terms of financial services. The growth of London, and to a certain degree Edinburgh and Glasgow, as financial hubs has been a process of Britain’s excellent placement within the EU. It has full access to European markets but is not in the euro area. As the British Government flirts with destroying this extraordinarily advantageous position, much of London’s work could head to New York or Boston.

The reality of that happening has been gleefully acknowledged by the Trump administration’s incoming Commerce Secretary, Wilbur Ross. Mr Ross has chortled about how the US could benefit by taking business from the UK because of the “God-given opportunity” presented by Brexit. He is not alone. Mr Trump has stocked his cabinet with titans of industry, almost all white men who have made their careers negotiating the best business deals possible for their corporations. Secretary of State nominee Rex Tillerson has spent his life making Exxon one of the largest and most profitable corporations in the world, while Treasury Secretary nominee Steve Mnuchin is a former Goldman Sachs executive who made his fortune buying a distressed bank after the financial crisis of 2007. They will cut what they consider the best deal for the US and almost certainly take advantage of Britain’s weakened position in doing so.

To think otherwise is delusional. Before one rushes to the conclusion that this is a strong argument for Scottish independence, it is important to take a deep breath. Certainly, if Scotland developed pro-trade policies, and was able to remain in the single market and maintain relatively free trade with the UK, it could benefit economically from American trade.

The SNP’s policy of making Scotland the most highly taxed part of the UK, however, would probably have the opposite effect. The best comparison would be to Ireland. If Brexit leads to Scottish independence, but an independent Scotland has a less competitive economic position than, say Ireland, US trade will definitely head to Dublin. If the US will deal with the UK without sentiment, it will deal with an independent Scotland likewise.

Professor O’Brien has the chair in Strategic Studies in the School of International Relations at the University of St Andrews. This is the first in a series of articles this week that will analyse key aspects of the Trump presidency as they will affect the US and the wider world.