Philanthropist hedge fund manager Bill Ackman issued a grave warning that Trump’s ‘Liberation Day’ tariffs could mean “business investment will grind to a halt”.

Ackman, whose net worth stands at £7billion, said: “The President has an opportunity on Monday to call a time out and have the time to execute on fixing an unfair tariff system.”

Global stock markets plummeted on Monday morning as Trump ignored Ackman’s advice and continues to stand firm behind tariffs that Ackman said are going to be “severely negative”.

The billionaire said that America is “100% behind the President” when it comes to rebalancing trade imbalances between the US and the rest of the world. “But business is a confidence game,” Ackman said in via an X post. “The President is losing the confidence of business leaders around the globe.”

Placing “massive and disproportionate” tariffs on all economic partners means “launching a global economic war,” Ackman added.

Last week, Trump signed tariffs into effect that set a 10% baseline charge on imports countries around the world sending global markets into turmoil.

This morning, the FTSE 100plunged to a one-year low. Analysts have warned that the scale of disruption in global financial markets is one of the worst to be felt in decades.

The index, which tracks the country's top 100 listed firms, dropped by about 5% in early trading on Monday as a sharp sell-off kicked in shortly after markets opened.

The panicked mood was felt across Europe, with Germany's Dax index recording a drop of about 6.5%, and France's Cac 40 down around 5.3% in the morning.

Ackman who announced his endorsement for Trump shortly after the attempt on the President’s life said: “If on April 9 we launch economic nuclear war on every country in the world, consumers will close their wallets and pocketbooks, and we will severely damage our reputation with the rest of the world that will take years, potentially decades to rehabilitate.”

The billionaire is the CEO of New York based hedge fund Perishing Square Philanthropies invests in education, health and the environment.

On Monday morning Ackman said the US Sectary of Commerce, Howard Lutnick, “profits when our economy implodes”. He added that Lutnick’s business interests represent and “irreconcilable conflict of interest” with his position in the US government.

Ackmam urged people to begin “hunkering down” ahead of a self-induced, economic nuclear winter” but signed off his length warning to Trump by saying, “May cooler heads prevail.”