Possible Clues:

• Aliens enter telling me to get knotted
• Aliens landed -- let out by environmentalists
• The minute party starts in Mayfair, everyone notices weird guests?
• Imaginary extraterrestrials
• Martians, in some depictions
• Aliens in short race round caring for planet
• Mini taken by environmentalist crew (imagined threat to our planet?)
• Aliens seen crossing the road?
• Saucer contents?
• Minor environmentalists that are out of this world?