A declaration by Britain that it is developing the capability to carry out offensive cyber attacks against other nations has triggered criticism and astonishment among security experts.

Philip Hammond, defence secretary, said ahead of the Conservative party conference in Manchester that the UK was “developing a full spectrum military cyber capability, including a strike capability”. It was the first time any country has made such a sensitive statement in public.

In recent years, defence officials and experts across the globe have assumed that a number of advanced military powers – most notably the US, Israel, Russia, China and the UK – have developed the ability to destroy or sabotage other nations’ internet infrastructure as part of military planning and covert operations.