fighter jets

Today 2 fighter jets deployed to escort a Pakistan airline plane to Stansted instead of Heathrow due to a disruptive passenger. What can the fighter jets do They cannot shoot the plane down unless they thought it was a terrorist attackso why does a plane need an escort which has been diverted from its original destination.

As long as it kept on track to Stansted, and the special security area there, then it would be OK but if it deviated indicating that the pilot was not in control then the fighters would take action initially warning shots and if deemed a threat to London say it would be shot down, there would be no 9/11 in London.

It all sounds a bit suspicious and worrying to me this especially when they said there was not thought to be a terrorist concern.