Crystal Amber, the company's fifth-biggest shareholder, urged Gerry Aherne in a letter sent to him earlier this month to launch a strategic review "to determine how value can best be realised", Sky said.

The investor said in the letter Aherne had failed to sufficiently engage to build market confidence in the firm's prospects.

"We are concerned that the Cenkos franchise is struggling to build a broader, more recurring revenue base," Crystal Amber's founder Richard Bernstein was quoted as saying.

Cenkos and Crystal Amber did not immediately respond to requests for comment.

The stockbroker said on Tuesday it expected full year revenue to be materially below those recorded in 2017, as those revenue figures included some unusually large fees.

(Reporting by Rama Venkat Raman in Bengaluru; Editing by Alexandra Hudson)