Okay guys, I finally sent one. Tell me what you think (I tried to keep it brief, Bez! :) ) :
I am waiting for you to provide urgent information that can materially affect my life: the names of the people and the statements made about me that have caused you to doubt me and threaten to withdraw your association.
Without this information, how can I confirm or deny what is being said about me?
These malicious rumours are damaging me in my social circle, as your statements above display--you demand I confirm or deny these rumours and if I do not, you will discontinue associating with me, taking that as a silent confirmation of truth to the malicious rumours. This only shows the extent of the damage already done by the rumours--you are ready to believe, with no evidence, that they are true, if I do not respond to the accusations.
I want this defamation of character to stop and I warn you and the others to quit talking about me under penalty of law.