It has been 5 years since a British leader has visited Moscow. On the eve of the first visit since a Kremlin critic was killed in London, the website for the Russian Embassy in London was attacked by a distributed denial of service attack. British Prime Minister David Cameron has been very vocal in the past about the killing of Alexander Litvinenko who was poisoned in 2006 by radioactive polonium-210, but has worked in the last year since taking over as Prime Minister to mend the relationship with Russia and President Dmitry Medvedev. “Prior to the visit of Prime Minister David Cameron to Russia,…