When a senior figure in the government called the White House on Wednesday morning to find out how bad Donald Trump’s tariffs were going to be for Britain, information was scant. Even Trump’s aides were in the dark about what he would decide. At 9pm that evening, Sir Keir Starmer sat down in 10 Downing Street and watched the television, just like the rest of us, to discover what the US president had in store. The blanket tariff of 10 per cent on imported British goods was half what Trump slapped on the European Union — but they still wrecked...