Gary Lager is correct.
Firstly the blame is not with the airlines, it is with BAA who insist that airlines will loose their slot if 80% frequency is not conformed to. They know that the airlines have to continue to operate using this slot empty. They are quite happy to rake in the additional landing fees knowing that it is costing the airline thousands of pounds and contributing to the CO2 emmisions.
Secondly, there are plenty of other airlines that are forced to do this as well. With the 'Open Skies' policy upcoming these empty services are more and more likely to occur as airlines are forced to operate somewhere or loose the slot that will have doubled in value when the Americans arrive.
If the Government are to do something, they should first knock on BAAs door. Of course they are less likely to do this as BAA handle so many passengers of whom the Government creams off so much money in taxes. Many of which are tourists and not actually UK citizens.