In March 2018, Salisbury became the epicentre of an unprecedented national emergency. A man and woman were found unconscious on a bench in the tiny city, sparking a major crisis when officials discovered the pair had been poisoned with Novichok - a chemical weapon developed by Russia.

Alexander Litvinenko was a former Russian spy who became a British-naturalised Russian defector.

Born in 1962 in Russia, Litvinenko served as an officer of the Russian FSB secret service who specialised in tackling organised crime.

He first became an informant in 1986, when he was recruited by the KGB counterintelligence section before he was transferred to the Third Chief Directorate of the KGB, Military Counter Intelligence, in 1988.

Later that year, he became an operational officer - serving in KGB military counterintelligence until 1991.

From then he rose through the ranks - until a fall out with none other than Russian President Vladimir Putin.

Putin and Litvinenko clashed after Litvinenko repeated claims from Boris Berezovsky that FSB officials had ordered an assassination attempt on his life during a press conference.

He was dismissed straight after - which Putin later said he personally ordered himself.

The Russian premiere said: “"I fired Litvinenko and disbanded his unit ...because FSB officers should not stage press conferences. This is not their job. And they should not make internal scandals public.”

Litvinenko was ordered not to leave Moscow - but in October 2000 the former sky and his family travelled to Turkey.

There, his application for asylum was denied, so Litvinenko bought air tickets for the Istanbul-London-Moscow flight - asking for political asylum at Heathrow Airport during his transit stop on November 1, 2000.

His application was approved in May 2001. Litvinenko became a journalist in London and an author, and campaigned alongside Berezovsky against Putin’s government.

On November 22, 2006, Litvinenko's medical staff at University College Hospital said he suffered a "major setback" due to either heart failure or an overnight heart attack. He died the following day.

Before his death, Litvinenko said: "You may succeed in silencing one man but the howl of protest from around the world, Mr Putin, will reverberate in your ears for the rest of your life.”