A chauffeur who works for the City PR heavyweight Roland Rudd was questioned by financial regulators as part of an investigation into insider dealing, it has emerged.

The driver is understood to have been interviewed about eight months ago with the full cooperation of Rudd’s PR firm, Finsbury, whose staff have since been informed. Senior executives were later questioned about his role.

In an internal memo, Finsbury’s managing director, James Murgatroyd, wrote: “I want to let you know that Roland’s driver has been interviewed by the Financial Conduct Authority in relation to a share-dealing investigation.

“He has not been charged with any wrongdoing, and there is no suggestion that he dealt or profited personally. Finsbury is cooperating fully with the FCA’s investigation.

“You know how seriously we take our adherence to the highest standards of ethics and governance – this is paramount for our clients’ trust in highly important and sensitive situations. It is everyone’s personal responsibility to uphold these standards.

“You will understand that legally we cannot make any other comments at this stage. You may confirm to clients what’s in this note and make clear that this is an isolated event.”

The interview with the chauffeur, first reported in the London Evening Standard, is understood to be part of a wider inquiry into insider dealing in the City. There is no suggestion that the driver or Rudd have done anything wrong.

Rudd, brother of the former home secretary Amber Rudd, is one of the most influential power brokers in the City. His firm provides public relations advice and crisis management communications to some of Britain’s biggest companies and often works on multibillion pound takeovers.

More recently, Finsbury has advised the board of its own parent company, WPP, on the fallout from an investigation into the conduct of the advertising company’s founder, Sir Martin Sorrell, who resigned in April.