Porton Down, Britain's top secret military research centre, is just a few miles away from where Sergei Skripal and his daughter Yulia were poisoned in Salisbury in 2018.
Yulia Lemeshchenko, 41, is seen testifying in an FSB video, but it is not known if she was put under pressure to confess to recruitment during the war.
Andrei Kelin, the Russian ambassador to the UK, said he hopes the former spy and his daughter are 'alive and well' as he demanded information about the pair.