For those who claimed Boris Johnson would be Donald Trump’s poodle, the past month has been corrective. Far from bowing before American power, he is defying it.

Johnson is considering rejecting America’s demand to ban Huawei from supplying parts of a new UK 5G network. His government is willing to override Trump’s objections and ensure the US tech giants pay more tax. Meanwhile the usually voluble Johnson has noticeably failed to offer loud support to Trump’s destruction of Barack Obama’s nuclear deal with Iran, preferring to ally with France and Germany instead.

Johnson is not only showing that his left-wing critics failed to understand him, but honouring the promise he made to millions of supporters of Brexit. Why shouldn’t Britain set its own tax policy and decide on its own foreign and security policies as it makes its way in the world? On Friday we will become a free and sovereign state once again, beholden to no one.

The trouble with the world Brexit has thrown us into, is that it is not a collection of sovereign states. The world, or most of it, is dividing into rival blocs. If not quite the Oceania, Eurasia and Eastasia of George Orwell’s imagination, then something close. We are about to discover that China and the US not only offer no favours in trade talks but use trade as a weapon to compel political compliance.

Imagine if Britain were to bow to Washington’s demands and exclude Huawei from UK 5G contracts. In all probability, China would not accept that a sovereign state was entitled to set its own security policy. Trade with China is now so important for so many countries it can follow Sun Tzu’s maxim that ‘ultimate excellence lies not in winning every battle, but in defeating the enemy without ever fighting’. China doesn’t separate economics and foreign policy. Trade is war by other means.

To take the most grimly preposterous example, look at how Pakistan, the Arab world and the Muslim republics of Central Asia stay silent on the internment and torture of China’s Uighur minority. They bite their tongues because they hate the economic losses alienating Beijing would bring, more than the mass persecution of their Muslim brothers and sisters. Westerners who remember the threats that came from Muslim majority countries when Danish cartoonists merely published cartoons of Mohammed, will have listened with incredulity to the meekness with which Pakistani Prime Minister Imran Khan confessed last week that he didn't ‘know much about’ the state terror in Xinjiang. Nor did he show any inclination to learn more. 'We are really grateful to the Chinese government’ for the economic aid China had given Pakistan, he said as he explained his wilful ignorance away.

You can focus on the obscenity of Muslim-majority governments organising vicious protests against cartoons while ignoring crimes against humanity, but the power politics should be your real concern. Denmark and the European Union would never have responded to attacks on freedom of speech with sanctions. But the Chinese communist party, from banning the exports of rare metals to Japan after the arrest of Chinese fishermen, to stopping imports of Norwegian salmon after the Nobel prize committee honoured the dissident Liu Xiaobo, has given every indication that it sees trade as a weapon to use against states that cross it.

Stephanie Hare, a British academic and technology expert, predicts the Chinese response to a British ban on Huawei would be: ‘we will punish you on trade and investment’. No one can say if she is right. Yet everyone must agree her case is more than plausible. But – for this is the price of living with aggressive superpowers – if we don’t ban Huawei or toe the line on Iran or lay off the tech giants, there is an equally plausible threat that the US will punish us in turn.

The Johnson administration's promise to implement a 2 per cent tax on the revenue of tech companies led Trump’s Treasury Secretary, Steven Mnuchin to respond: ‘If people want to arbitrarily put taxes on our digital companies, we will consider arbitrarily putting taxes on car companies’. The US has warned the UK that intelligence-sharing arrangements would be at risk if the Huawei deal goes ahead. Trump ‘is watching closely,’ his officials warned.

As for Iran, Richard Goldberg, a former member of the White House national security council told the BBC: ‘The question for prime minister Johnson is: “What are you going to do post-31 January as you come to Washington to negotiate a free-trade agreement with the United States?’”

Just as China uses its power in world trade for political ends, so Trump uses the power of the dollar and American dominance of the global financial system to punish not just China but also Iran, Russia and a host of others—including allies such as the European Union and Turkey. Secondary sanctions target anyone who trades with America’s enemies, even if their government says the trade is lawful.

Does the British government know this? Senior civil servants, with a fine contempt for Dominic Cummings’ gagging orders, say ministers ‘don’t have a clue'. ‘A campaign slogan is not a plan,’ said one. The ex-senior civil servant and ambassador to the EU, Sir Ivan Rogers, warned in November that Johnson’s promise to ‘get Brexit done’ in a year risked repeating Theresa May’s mistake. ‘Because we are under time pressure and known to be desperate to "escape vassalage" by the end of 2020… the EU side just sees a huge open goal’.

The EU will make its own political demands on Britain on state aid for industry, for instance, and environmental and workplace standards before it grants a trade treaty. From the British point of view, the significant difference between the EU and China and the US, was that Britain was a member of the EU and could help set the rules it had to follow. On Friday we leave, and nothing this government has said or done shows that it begins to grasp how cold it will be outside.