The United Kingdom sentenced two people to prison on Thursday after they were convicted of spying on behalf of China, renewing concerns about Beijing’s influence in the country.

Former Hong Kong Police Superintendent Bill Yuen and U.K. Border Force officer Peter Wai were sentenced to a combined 18 years in prison, according to an order from Judge Bobbie Cheema-Grubb, who presides over London’s Central Criminal Court. The pair worked in tandem on behalf of Beijing to carry out a “shadow policing operation” targeting Chinese pro-democracy dissidents, or “cockroaches,” living in the U.K., according to prosecutors.