When the Cold War ended, it didn't spell curtains for the secret agent. Private espionage is a booming industry and environmental protest groups are its prime target.

As you hunker down for the last few days of the Camp for Climate Action, discussing how to force your way into Kingsnorth power station in an attempt to prevent the construction of a new coal facility, cast your eyes around your fellow protesters. Do they look entirely bona fide to you? And don't look for the old-school special branch officers - Kent Police are a tiny force. It's the corporate spies hired by private companies you need to watch out for.

According to the private espionage industry itself, roughly one in four of your comrades is on a multinational's payroll. ....