By the way, this [poisoning] has been the style of the British special services for the past several centuries. Already in the 16th century, British doctors poisoned Ivan the Terrible and his son, Ivan.
Conspiracy theory and recurring pro-Kremlin disinformation related to the UK secret services in order to confuse the audience about Russia being behind the Salisbury attack.
According to Britannica, Ivan the Terrible murdered his only viable heir, Ivan, in 1581.
Nothing suggests on British doctors' role in the Ivan the Terrible's death. www.biography.com/people/ivan-the-terrible-9350679,
For further debunking see Myth Detector.