Theodoros Angelopoulos, a Greek steel and shipping billionaire, is understood to hold a stake in Swiss bank UBS of between 6% and 9%, which is worth as much as Sfr5bn (£2.5bn), according to a Swiss newspaper.

Tagesanzeiger, a Swiss broadsheet, claims Angelopoulos' family was the largest private investor in UBS in 1998, citing internal documents, and that he continues to hold a stake. The position has never been reported.