Haven't heard any more about it since this:

BBC NEWS | UK | England | Sussex | Man in court after Heathrow alert

Looks like it could have been a failed terror attack, but it could also have been a protest against plans to build a new runway...
McLeodGanja Reviewed by McLeodGanja on . Brits Arrest Man at Heathrow Airport! On the news now....sounds like the dude jumped a fence with a backpack and ran out on the runway. They did a controlled explosion on it from reports. Have a SAFE one!:jointsmile: Rating: 5