Even the method ssuggested by Mr Gabriel may be of limited use as refusal of concent by third party is not the sole ground for refusal of information. CIC has decried this tool to be used to suppress disclosure which will lead to exposure of corruption. You think that the may use the information for personal or political ends he may use it to expose corrution in your department. So your stand may be against public policy. Using information for personal and political use is different that using it for anti-national activity. You are not able to intimate as to what type of information is there and how it can cause industiral unrest. Industrial unrest has been caused by RTI applications on Commonwelath games, 2G case, Aadarsh society. You are yourself admitting that the person is careful enough that his application is not hit by section 8. The aim of RTI is to compell honesty and efficienty in Govt offices and the person may pehaps be a tool in the direction.