Russia is still very much a security threat inside the UK

At 1.30 p.m. on 7 September 1978, Georgi Markov, a Bulgarian dissident and BBC journalist, approached a bus stop at the south end of Waterloo bridge. As he gazed absent-mindedly across the Thames, office workers jostled him as they streamed past. Suddenly he felt a sharp pain on the back of his right thigh. Turning quickly, he saw a man stoop to pick up an umbrella. ‘I am sorry’, the man mumbled in a gruff foreign accent. Seconds later, a taxi pulled up, the man jumped inside and disappeared. 

The pain was excruciating, and Markov was taken to St James’ hospital, Balham. As he lay in bed, the Soviet bloc defector mentioned the incident, but the doctors did not suspect foul play and thought he had a high fever. Four days later Markov died. At first the autopsy did not reveal anything sinister. But then a fragment of tissue at the puncture mark was sent to a special laboratory at Porton Down, Wiltshire, where they discovered he had been poisoned by ricin, a lethal derivative of the castor oil plant.