When Andrew “Twiggy” Forrest landed in London last weekend, he was sporting the same blue suit and yellow tie he has worn for trips to Europe ever since Russia invaded Ukraine.

Dressed in the colours of Ukraine’s flag, and wearing a flag badge on his jacket lapel, there can be no doubt about whose side the Australian billionaire and mining magnate is on.

Forrest is Australia’s second-richest man with a fortune estimated at $20bn (£15bn), and is one of the few major business figures to pledge to provide meaningful financial support to help Ukraine’s post-war reconstruction.

The $500m that he committed in the months that followed Vladimir Putin’s invasion quickly became the bedrock for a global fund described as Ukraine’s “Marshall Plan”, in a nod to the US economic aid that paid for reconstruction of Europe in the aftermath of the Second World War.

Yet the prospect of Donald Trump and Putin carving up Ukraine’s territory between themselves in the face of fierce opposition from the Ukrainian government has prompted Forrest to threaten to tear up his pledge.