BBC director general Mark Thompson has expressed regret for not consulting trustees over signing an open letter about BSkyB's future, it has emerged.
At a recent meeting of the BBC Trust, chairman Sir Michael Lyons said he was concerned whether Mr Thompson's action had been "appropriate".
Mr Thompson admitted he had not discussed the issue with the BBC's governing body but "should have done".
The letter warned against Rupert Murdoch's proposed buy-out of BSkyB.
Numerous broadcasting and newspaper heads signed the letter to Business Secretary Vince Cable expressing concern that News Corporation's plans would leave other outlets unable to compete with them.
Mr Thompson expressed regret at the 21 October meeting about his failure to consult the trust before signing the letter, but a trust spokesman added that trustees made no comment about its contents.
Mr Thompson did not regard his action "in any way inconsistent with the BBC's duties of impartiality," the spokesman added.
Mr Cable has since ordered media regulator Ofcom to investigate the proposed takeover of BSkyB.