The Chief of MI6 has urged Russia "not to underestimate our determination and our capabilities" following this year's nerve agent attack in Salisbury. Speaking at the University of St Andrews on Monday, Alex Younger described how MI6 helped expose the perpetrators said to be behind the attack, and how it helped co-ordinate the expulsion of Russian diplomats. Report by Jonesia. Like us on Facebook at http://www.facebook.com/itn and follow us on Twitter at http://twitter.com/itn