Overnight at least 18 countries have said they will expell Russian diplomats in the wake of the poisoning of former Russian spy Sergei Skripal. More than a 120 diplomats will be sent home, sixty alone from the US. The UK expelled 23 diplomats earlier this month. Addressing the House of Commons just before UK Prime Minister Theresa May said it was important to send a strong and united message to Russia. Russia has hinted it will respond with "symetrical" measures and the Kremlin is expected to make an announcement in the coming days. Correspondent in Washington Harry Horton discusses the details with Susie Ferguson.