On May 30, US President Donald Trump declared a new trade policy on Twitter. “On June 10th, the United States will impose a 5% Tariff on all goods coming into our Country from Mexico, until such time as illegal migrants coming through Mexico, and into our Country, STOP,” Trump tweeted.

Seconds after reading the tweet, a London hedge fund manager sprang into action. Sensing a new US trade dispute, and recognising that trade war threats often result in investors fleeing to safe-haven assets, he immediately increased his position on Treasury bonds, making a “six-figure sum” when the bond market rallied. “Thanks to that tweet, I entered June in a very good mood,” said the manager, who asked to remain anonymous.