THE South China Morning Post Group announced yesterday that Sunday Morning Post editor Peter Lynch was leaving the company. Post general manager Gene Swinstead said Mr Lynch had made a major contribution to the success of the Sunday Morning Post since becoming editor two years ago, including the highly successful launch of the new Sunday magazine. ''We are sorry to see him go and wish him and his family well,'' Mr Swinstead said in a statement. Mr Lynch is considering an offer from News Ltd in Australia. Meanwhile, David Armstrong has been appointed acting editor-in-chief responsible for both the daily and Sunday newspapers.