Why can't these planes at Heathrow just take-off?

The plane's OK. They are designed to fly at 30,000 feet where the temperature is -30 C. The problem is with ice on the runway and taxiway. Controlling a plane on the ground is like trying to steer a child's tricycle with a couple of rockets. The plane could easily skid sideways and the first thing that gets damaged are the fuel tanks in the wings - and that stuff can explode. A sideways skid on the runway during take-off could cause the plane to cartwheel - great video for youtube, but fatal for the pengers and crew.