Boris Johnson has insisted that military intervention in Afghanistan over the last 20 years was "successful" and that British troops did not die "in vain". br br Appealing to the families of fallen personnel, the prime minister said the combat reduced terror threats in the West and allowed millions of girls to be educated. br br "What I would say to those families now is, I understand what you feel, but I believe that it was right, it was worth it," he said. Report by Buseld.