When Helen digs out some old letters from her former partner John, she finds some potential clues.

In 1986, members of environmental group, London Greenpeace, published a leaflet called ‘What’s wrong with McDonald’s?’ It claimed McDonald’s was exploiting workers, destroying rainforests, torturing animals, and promoting food that could make people sick, even cause cancer...

McDonald’s said the claims in the leaflet were untrue and defamatory and the company demanded an apology.

Helen Steel, a gardener, and a former postman named Dave Morris, refused.

Mark Steel takes us into the murky world of McDonald’s Corporation vs Steel & Morris – aka 'McLibel' - the longest-running trial in English history which would turn the spotlight on the way big business operates. As well as bringing issues like rainforest destruction and advertising to children into the mainstream, it would also be the moment our current Prime Minister first comes to prominence. If that isn’t enough, this story would ultimately have connections with a dark and shameful secret at the heart of the British state - something which Mark discovers he himself had been a victim of.

Shadow World: Gripping stories from the Shadows – BBC investigations from across the UK.

Presenter: Mark Steel

*Archive excerpts from director Franny Armstrong’s ‘McLibel,’ reproduced with the permission of Spanner Films