BT investor Patrick Drahi has said that he “feels betrayed” over an alleged corruption scandal within his telecoms empire that triggered the arrest of his right-hand man.

The French billionaire said that he was “shocked” after Portuguese authorities launched a criminal investigation into alleged corruption by individuals and senior executives within his sprawling media and telecoms group.

Mr Drahi and his company Altice have not been implicated but the scandal has prompted an internal review on top of the Portuguese judicial investigation.

Speaking about the scandal for the first time, he said: “This has come as a shock and as a huge disappointment to me. If the allegations are true, I feel betrayed by a small group of individuals, including one of our oldest colleagues.”

Armando Pereira, Altice’s co-founder and Mr Drahi’s right-hand man, was last month placed under house arrest while the investigation is conducted, his lawyer said. He has denied any wrongdoing.

Talking to investors on Monday, Mr Drahi cast Altice as a victim in the alleged fraud and said that the company has placed 15 employees on leave in Portugal, France and the US amid the investigations.

He added: “It is very unpleasant to see the name of ‘corruption’ next to the group… and next to my name.

“I assure you that we take this matter very seriously, and we are taking swift proactive action to understand the truth and protect the group from any harm in the event that the allegations are substantiated.”