Comment by LincolnedList

It depends. If ISIS does it to scare the UK into a political decision because it has no way of matching its military in the battlefield (e.g to push out UK forces in Iraq) its a Terror attack in nature.

If it is actually done to degrade the capabilities of the UK military so ISIS could use its fighters to chase them out of Iraq, or maybe, conquer a part of England - its an act of war and is actually worse from a UK POV. Calling it a terror attack would be silly.

People are biased to treat wars as better then terror because wars have rules and often involve good people trying to defend their country. But from a country's POV a terror organization is usually way less dangerous than a competent enemy military attacking.

Terror is usually done because someone lacks military competence and is willing to play dirty to even the playing field.

The establishment is so aggressive in condemning terrorism, because its easier to deal aggressively with a small terrorist organization before it becomes an established military and carves its own autonomous place on the world stage.

ISIS is a good example, it used a lot of terror tactics, but its goal was to create a country.