"Alien Invasion" has been created by HHCL/Red Cell and shows a group of aliens discussing a takeover of Earth, debating whether or not it is a worthwhile investment.
Aping the start of 'Star Wars', text appears on a screen telling us "In a galaxy far, far away, orbiting in a galaxy close to Thyrius" before cutting to a Death Star-like battle station.
Broadbent, who won a Best Supporting Oscar for his role in 'Iris' in 2002, plays the leader of a council of aliens sitting at the heart of the station, echoing an early scene in Star Wars, who are debating whether they should invest in a takeover of the Earth.
Izzard plays a hardened cynic who says Earth is about to fall apart like "a pig in a blender" and that it is a "crap sandwich" whose leaders are insane. He lists a whole series of reasons for not taking over in his presentation, including "their self-assembly furniture always has one bit missing".
However, another alien, played by the Scottish actor Joe McFadden, best known for 'The Crow Road', defends the planet, saying that 90% of the population wants to help save the environment. His list of plusses for invasion include "sunrises and sunsets", "it also has 'The Simpsons'" and "cold and warm beer".
The ad features many humorous touches, with Izzard describing email as "an early distribution system for pornography" and Broadbent reeling in horror when he is shown a picture of George W Bush, who is described as earth's "top man". He also says "we've been sending them a map for 30 years in cornfields and what have we got back?".
The environmental charity says that it has turned to humour as a means of communicating its message because it hopes to motivate armchair activists.
Steven Henry, creative director at HHCL/Red Cell, who wrote the script with Jason Macbeth, described the approach as revolutionary.
"We have aimed to make 'Alien Invasion' an entertaining and inspiring way of communicating Greenpeace's message and make people feel positive and empowered rather than guilty and helpless," he said.
Greenpeace paid nothing for the campaign, which was directed by US director Hank Perlman through his production company Hungry Man. Perlman organised the two-day shoot, while the London-based post-production company, The Mill, donated hundreds of hours working on the special effects.
John Sauven, special projects director at Greenpeace, said: "The finished article works on a number of different levels. It entertains rather than scares, it doesn't use cliched images and it highlights that individuals can make a difference."
The ad will be distributed and will be shown throughout UK cinemas on several November film releases with the support of Pathe Films.
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