In chapter 49 Mr Gardiner writes a letter to tell the Bennets about Lydia. He writes that he knows where Lydia is and that he has seen her. He also writes: "The particulars I reserve till we meet: it is enough to know they are discovered."

Then Lydia comes home and slips to Lizzy that Mr Darcy had been present at her wedding but that it was supposed to be a secret. Lizzy writes to Mrs Gardiner who is surprised that Lizzy is ignorant and readily tells her all she knows. When Lizzy thanks Mr Darcy for helping Lydia he says: "I did not think Mrs Gardiner was so little to be trusted."
It seems that Mr Darcy intended for his services to be kept a secret, yet both Mr and Mrs Gardiner has no hesitations to tell the story to the Bennets. I read the first quote from Mr Gardiner as a willingness to explain but the stress for time prevented him from a lenghty explaination. Even Mrs Gardiner thinks she must devote a whole morning to answer and we know how long a Regency morning was.
With this in mind I am thinking about confidences. Jane and Lizzy has shown very high standards when it comes to information they have recieved in trust. Are Mr and Mrs Gardiners standards at fault here as they are telling/intends to tell the particulars about Mr Darcys involvement?