Thank you, HoltCJ, for your very level although somewhat guarded reply. Your presence in this forum should prove highly educational to many of us.
On this side of the Atlantic, defamation of character is regarded as a serious offence and has resulted, when successfully prosecuted, in quite large sums of money changing hands. As you quite rightly pointed out, however, the burden of proof rests with the plaintiff.
May I refer to my original question; in the absence of documented proof, what avenues of pursuit are open. Recorded telephone conversations perhaps, sworn testimony from fellow pilots?