LONDON -- The mayor of London had a narrow escape Thursday -- from some angry clowns. The pie-wielding clowns had waited to ambush Ken Livingstone outside a city hall building. The clowns planned to pelt Livingstone with custard pies to protest a new traffic-reduction plan. The pie-packing performers said a new charge on motorists will hurt their touring circus. The mayor managed to miss the clowns, but officials refused to say whether he entered city hall through a back door.