The following links provide further sources of useful information:
https://www.cpni.gov.uk/espionage
https://www.mi5.gov.uk/espionage
https://www.gov.uk/report-suspicious-activity-to-mi5
https://www.fbi.gov/investigate/counterintelligence
https://www.fbi.gov/history/famous-cases/espionage-in-the-defense-industry