Attack against a NATO ally or UK deployed forces which meets the Article 5 threshold


The North Atlantic Treaty Organization’s (NATO) purpose is to guarantee the freedom and security of its members through political and military means. NATO is committed to the principle that an attack on one or several of its members is considered as an attack on all. This is the principle of collective defence, which is enshrined in Article 5 of the Washington Treaty. So far, Article 5 has only been invoked once, in response to the September 11th terrorist attack in the US in 2001.


The reasonable worst-case scenario involves a hostile state launching an invasion of a NATO ally or an attack on UK deployed forces, which causes NATO allies to unanimously invoke Article 5 of the Washington Treaty. NATO activates its response plans but hostile state forces are not ejected and the crisis continues. There is disruption to UK and European economies as economic ties with the hostile state are severed. There would be large numbers of casualties and fatalities.

Although the scenario is not UK based, there are likely to be some British Nationals involved. Depending on the region where the crisis occurs, there could be severe disruption to gas supplies.

The position on the matrix is held at a higher classification.

Response capability requirements

This would require a full range of military, diplomatic, economic and information capabilities to contain aggression and deter further aggression.


This event would result in impacts lasting several years. Economically, the disruption to global markets (depending on the location) could be impacted by disruption of supply chains, reduction or prevention of fuels (gas and oil) and global economic instability.