LONDON (AFP) - A protester threw green custard in the face of British business minister Peter Mandelson on Friday, in a stunt to highlight opposition to a new runway at London's Heathrow airport. Mandelson was arriving for a summit on carbon strategy when protester Leila Deen approached him and hurled a large cupful of custard straight in the former European Union trade commissioner's face. Mandelson bent down, turned away and walked inside, while the protester picked up her papers off the floor and calmly walked off - to be interviewed a short time later on television stations. "Mandelson is trying to make political capital out of climate change," said Deen, a member of the group Plane Stupid which has staged a number of protests over the British Airports Authority's plans to build a new runway at Heathrow. "The only thing green about Peter Mandelson is the slime coursing through his veins. "The third runway is an insult to my generation," she said, adding: "We can't let the 'Prince of Darkness' cast his shadow over west London" - a reference to Mandelson's nickname earned for his media spinning skills. Mandelson, a former EU commissioner who returned to the British government last year, seemed unfazed by the stunt, and went on television shortly afterwards - minus his splattered coat - to downplay the incident as an "adolescent protest". "She was so busy throwing what seemed like green soup or something in my face that she failed to tell me what the protest was about, but as you can see thankfully is wasn't paint and I've come through it intact," he said. Deen, 29, was one of three Plane Stupid protestors who tried to drown out a speech by Transport Secretary Geoff Hoon at an environmental conference earlier this week, by sounding horns.