Imagine finding a GPS tracker underneath your car - that's what happened to Corin Smith, an environmental campaigner.

Although he didn’t find the people who placed the device under his vehicle, he later discovered that a company he'd criticised had hired private detectives to monitor him.

There's been a long history of undercover policing of environmental groups, but should private companies be allowed to hire spies to carry out surveillance on individuals who criticise them?

We met some of the campaigners who've been targeted and say they have had their movements tracked.

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