It's 8am, it's freezing cold and I'm about to dump a lorry load of coal on the doorstep of the Prime Minister. Just a typical day in the life of an activist for Greenpeace, the world's biggest and best-known environmental campaigners. They're hoping I'll help them score massive publicity coup – one that will embarrass a government breaking its promises over climate change. What they don't know, however, is that I'm a double agent.. And if everything goes to plan they're walking into a trap – one of my making.

When ex-Paratrooper and policeman Ross Slater took on a close protection security job for Greenpeace he got more than he bargained for. Soon he found himself a double agent, spying on his eco-warrior paymasters for Special Branch and ultimately a government twitchy about any kind of protest activity on British soil.

During five explosive years as an insider, Slater immersed himself in the radical lifestyle of the environmental activist, blurring truths and lies and battling to stay straight while drug taking and a free love spirit went on around him. In that time he was taken hostage, caught plotting an attack on a nuclear power station and nearly arrested outside No.10. But all the while he provided UK law enforcement with the most comprehensive breakdown it has ever received of the organisation's global hierarchy.

The role of undercover police officers in environmental groups has been brought into sharp focus following a recent and now Slater gives a unique perspective on what it takes to be an undercover agent and how our government spies on green groups.