Britain warns Russia over double agent's mysterious illness

By Toby Melville and Emily G RoeSALISBURY, England (Reuters) - Britain warned Russia on Tuesday of a robust response if the Kremlin was behind a mysterious illness that has struck down a former double agent convicted of betraying dozens of spies to British intelligence.Foreign Secretary Boris Johnson named Sergei Skripal, once a colonel in Russia's GRU military intelligence service, and his daughter Yulia as the two people who were found unconscious on Sunday on a bench outside a shopping center