Amesbury Novichok poisoning
Germany says there is 'unequivocal proof' that Russian opposition politician Alexei Navalny was poisoned with the nerve agent
By Steven McIntosh
By Gordon Corera
By Jordan Davies
Former Russian spy Sergei Skripal and his daughter Yulia were targeted with the nerve agent.
By Olga Ivshina
BBC Russian Service
By Mark Urban
Diplomatic and defence editor, Newsnight
Ahead of one-one-one talks with Vladimir Putin, Mrs May speaks about the Novichok poisoning.
The BBC was given access inside Porton Down, where some of the world's deadliest viruses are researched.