It’s Greenpeace. They’d like us to come in to make a film about something “big”. One of their major campaigns at the moment is to stop a multinational oil company, Shell, from drilling in the Arctic. Big in this context usually means enormous.

A series of “phones off, no notes, and from now on you only refer to this project as xxxx” meetings commence. We're to turn up at Greenpeace’s North London warehouse in the beginning of June to begin filming what would become the most daring urban climb this side of King Kong.

I met Liesbeth, Ali, Victo, Wiola, Sabine and Sandra. Six women selected from around the world who “climbed a bit” and wanted to save the Arctic. So they decided to use the tallest building in Europe as a massive billboard directed at the public and – crucially – Shell. A picket outside an AGM is alright, but those are usually ignored. Scaling a mahoosive glacier-like structure in the middle of London over climate change and Arctic drilling would grab far more attention – and seal itself into the public consciousness.

Working with Greenpeace is a bit like signing an environmentalist official secrets act. And because nobody really knows what everyone else is doing until they’re about to do it, you become accustomed to talking in coded circles – which I’m told is part of life on planet Greenpeace. “Sigmund” was the project’s code name…a well-thought-out Freudian pun. And one of the climbers has a serious fear of heights. But there is very little else I’m sure I can tell people…and there’s very little that needs to be said.

Here’s the film.