Daily Minister: He’s had egg on his face several times before. But never, until yesterday, custard. Lord Mandelson was splattered with a face-full of the stuff as he stepped from his ministerial car. A protester, angry over expansion plans for Heathrow Airport, hurled the green-tinted custard at him while shouting: ‘That’s for the third runway!’ The stunned Business Secretary, who was without police protection, staggered away with his overcoat, scarf and tie soaked in bright …