CCTV footage allegedly showing Sir Frederick Barclay's nephew handling a bugging device at London's Ritz hotel has been released.
The footage is at the centre of a bitter legal row between the families of the billionaire Barclay twins.
Sir Frederick, 85, and his daughter Amanda are suing three of Sir David Barclay's sons for invasion of privacy.
They claim the surveillance gave the men commercial advantage and they sold the Ritz for half its market value.
The Barclay brothers' businesses include the Telegraph Media Group, the online retailer Very Group, the delivery business Yodel, and - at the time of the bugging - the Ritz hotel in London.