Hardy Underwriting's aviation class underwriter John Spence has left to join its part-owned rival, Atrium.
Hardy owns 23.6% of Atrium - an investment which has earned it considerable attention recently as its value has soared.
Spence's move was seen by some in the market as lending credence to Hardy's statements that it does not intend to buy Atrium.
Sources close to the company suggested Spence made his move after he was lured by an attractive profit commission deal and a desire to make a name for himself outside the Hardy organisation.
Hardy made a shrewd move with the Atrium purchase at 75p a share in November last year and has seen the stock increase in value to about 163p.
Hardy has consistently said it does not intend to make a bid for Atrium but regards its stake as an investment.