The origin of the mysterious nerve agent, used on March 4 to poison former Russian double-agent Sergei Skripal and his daughter Yulia in Salisbury, has been the main point of contention in the unraveling international scandal. While Britain claims that the alleged A-234 nerve agent – also known as Novichok – was a Soviet development and thus could only have been used by Russia, Moscow contends that the chemical has since been studied by numerous parties and could have been re-engineered elsewhere, including in the UK itself.

Last week, in an interview with the BBC, Russia's ambassador to the EU, Vladimir Chizhov, noted that a secret military research lab at Porton Down, which is located roughly seven miles from the scene of the incident, could have manufactured the deadly agent. Among its other military-related research, the Defence Science and Technology Laboratory (DSTL) specializes in Chemical, Biological and Radiological warfare.