IT is a matter of record that the Chinese for reasons of their own distrust Governor Chris Patten. But judging by this little tale causing a quiet chuckle in Beijing, it seems as if some of the venom is being shifted in the direction of Britain's Ambassador to China, Sir Robin McLaren. A man parks his bicycle outside the British Embassy and is walking away when he is accosted by a PLA officer. Officer: ''You mustn't leave your bike there. Don't you know the British Ambassador lives in that house?'' Cyclist: ''Don't worry, officer. I've chained it up.''