When Alistair allegedly planted the device in January, the two sides were conducting separate negotiations. Because of the recordings, the cousins were able to learn that Saudi Arabia-based Sidra Capital had made an initial offer of 1.3 billion pounds to Frederick and Amanda as well as an unnamed acquisition being discussed between Frederick, Amanda and a Russian businessman, the pair’s lawyers said.

The cousins lawyer, Heather Rogers, said that they accepted that Frederick and Amanda were recorded without their knowledge or consent and that some of the recordings’ transcripts were shared between the cousins, who haven’t filed a defense. She criticized Frederick and Amanda’s written submissions for being purposefully “eye-catching and emotive” and using “heavy spin.” 

“This is a dispute about family members and from the defendants’ point of view it is unfortunate that they are being canvassed in public rather than resolved in the family,” she said at the remote court hearing earlier this month.

A spokesman for Frederick and Amanda declined to comment beyond their earlier statements. A spokesman for Ellerman Holdings Ltd., the holding company for the Barclays’ U.K. assets led by Aidan and Howard Barclay, also declined to comment.

Mystery Businessman

This month’s court hearing also revealed that David’s sons hired Quest Global Ltd., a private investigation firm with offices in London and Qatar, which supplied a separate bug, Rees, Frederick’s attorney, said in written submissions. Quest charged for 405 hours for listening and transcribing the recordings, which were then shared with the cousins, Rees told the court.

Quest, chaired and at least partially owned by the former London police chief John Stevens, is most well known for its work on sports investigations. It operates from an address just across the park from the Ritz, and boasts of its extensive experience in surveillance and long-term monitoring of staff and buildings. A representative for Quest declined to comment.

In court, Rees said the recordings captured extensive discussions between Frederick, Amanda and a mystery Russian businessman relating to an unnamed acquisition that didn’t go through after the cousins’ attorneys intervened. He said Quest delivered a report into the Russian businessman in November last year, apparently prepared for Ellerman Holdings.

Billionaire Twins

The 85-year-old twins are among Britain’s most discreet billionaires, known for a family compound on a tiny island off the U.K.’s southern coast.