"Serious organised crime"? Are we talking "traditional Chinese social institutions" here?
I heard years ago that there was an "understanding" - the law didn't look too closely as long as innocent people weren't disturbed - came after a gang burst into a restaurant in C London armed with cleavers etc and a pitched battle was fought around the customers (no serious injuries to the paying public but ...). In the good old days of Chairman Mao the TCSI's were a steady & reliable source of information on CCP activity in the UK and Europe I believe.