Of President Trump's many controversial initial moves in the White House – including his recent ban on travel to the US by nationals from seven Muslim-majority countries – his support for torture in interrogation is the most shocking.
Previous US administrations sought to argue that certain techniques, such as waterboarding, were not torture on the basis that they did not reach the required level of pain and suffering, even if that was a justification with which most would disagree.
Trump has a different view. While the new president also does not think that waterboarding amounts to torture, for him, that is not the point – because he favours going much further and adopting techniques "a hell of a lot worse". His belief is that "torture works".
This begs the question: could Trump ever face criminal prosecution in the UK or elsewhere for his support of behaviour recognised to be a crime by most countries in the world?
The UN convention against torture requires all parties to the convention – which include both the US and the UK – create a criminal offence within their domestic legislation covering torture. In the UK that offence is found in the Criminal Justice Act 1988.
The convention also requires that the offence should be one of universal jurisdiction. This means that a person who orders torture can be prosecuted in one country even though the act itself occurred elsewhere. For example, last year a Nepalese officer, Kumar Lama, was prosecuted – and ultimately acquitted – in England for torture said to have taken place in Nepal in 2005. There have been similar cases elsewhere in Europe.
As US president, Trump enjoys personal immunity from any criminal prosecution outside the US – but only for the duration of his presidency. After that, Trump would be criminally liable for certain categories of crime committed by him during his presidency. The case against Augusto Pinochet established that there is no immunity for a former head of state accused of ordering torture.
Of course, there are further reasons why it is highly unlikely that a prosecution of Trump in the UK would ever succeed. His support for torture – as currently expressed – is insufficient to create criminal liability in English law. And if he ever did give an order that could create such liability, presumably it would be supported by legal advice that such an order was lawful.
This could be sufficient to establish that he had "lawful authority, justification or excuse", which is a defence to a torture charge in the UK.
No doubt to the disappointment of some of his detractors, it is unlikely that Trump will be appearing at the Old Bailey charged with torture in the years ahead. But it is important that it is a legal possibility; and it is important that the UK can – and has – invoked universal jurisdiction to prosecute foreign nationals for torture in the past.
This, rather than the language of diplomacy, should underpin the UK's response to President Trump's pronouncements.
This article was first published by The Brief on 31/1/2017