It is a question that successive governments have struggled with: what kind of threat does China really pose to the UK?
Trying to answer it may have contributed to the high-profile collapse of the case in which two British men, Christopher Cash and Christopher Berry, were accused of spying for China and charged under the Official Secrets Act.
Both deny wrongdoing - but when charges were dropped last month, it sparked political outcry.
Prosecutors and officials have since offered conflicting accounts about whether a failure or unwillingness to label China as an active threat to national security led to the withdrawal of the charges. And yesterday Lord Hermer, the attorney general, blamed "out of date" legislation for the case's collapse.
But this all raises the question of what exactly Chinese espionage looks like in the modern world.
