Donald Trump must divulge detailed financial information from his many businesses as part of his $10bn defamation lawsuit against the British Broadcasting Corporation, a federal judge ruled during a discovery hearing on Tuesday, according to news reports.

The ruling by US magistrate judge Enjoliqué Lett could open a unique window into the hundreds of businesses owned by Trump’s family trust. It also highlights a potential drawback for Trump’s strategy of bludgeoning critical media with multibillion-dollar lawsuits.