Gobby diplomats

Sir Kim Darroch, is a very senior diplomat, head of mission in Washington as British Ambassador to the United States. As I understand it the first rule of diplomacy is keep your ears open and your mouth shut. Sir Kim has been unveiled as a man who has expressed his opinion that the Government of his hosts is disfunctional and inept. How stupid is that?
Whilst in post, the Ambassador should surely respect his hosts and keep such opinions to himself, both publicly and in private. There should certainly be no written evidence and any utterances conducted without recordings. As a consequence of his indulgence, Sir Kim is a lame duck Ambassador, ridiculed at home and derided by the President. There have been murmerings of support from Mrs May and other Foreign & Commonwealth figures but  quite frankly he should be withdrawn and sacked, a salutary message to other diplomats. The time to say these things is when he is retired from public life and writes his memoirs