LONDON - The poisoning of a former Russian double agent in Britain with a nerve agent last month shows "how reckless Russia is prepared to be," the head of Britain's GCHQ spy agency said on Thursday in a scathing attack on the Kremlin.In his first public speech since taking over as head of Britain's eavesdropping intelligence agency, Jeremy Fleming said the poisoning of Sergei Skripal and his daughter in Salisbury, southern England, demonstrated Russia's "unacceptable" behavior.Britain has blamed Russia for the attack while Moscow has denied any involvement. It has led to one of the biggest diplomatic crises between Russia and Western nations since the Cold War."You've heard it said, and I'll repeat, the attack on Sergei and Yulia Skripal in Salisbury, was the first time a nerve agent had been deployed in Europe since the Second World War," Fleming told a cyber conference in Manchester, northern England."That's sobering. It demonstrates how reckless Russia is prepared to be, how little the Kremlin cares for the international rules-based order."