March 4: Sergei Skripal, 66, and daughter Yulia, 33 are found unconscious in a park in the English city Salisbury. Emergency services are called to a suspected drugs overdose. But Mr Skripal is a former colonel in Russia's GRU military intelligence service who was convicted in 2006 of spying for Britain and imprisoned before he was handed over in a spy swap in 2010.
March 6: Counter-terrorism police are put in charge of the inquiry as suspicions grow that the pair, now in a coma in hospital, were targeted by Kremlin-sponsored assassins. Forensic efforts to determine the type of poison are undertaken by the nearby Porton Down scientific laboratory. Boris Johnson, the foreign secretary, tells the House of Commons that Russia as "a malign and disruptive force" that will face punishment if it is the source of the attack.
March 9: Fears of chemical contamination sees the search area widened from restaurants and shops to a city graveyard. Around 180 troops, including Royal Marines, RAF Regiment troops and chemical warfare specialists, are understood to have been deployed after Scotland Yard requested specialist help.
March 11: The authorities offer "precautionary advice" to diners in two Salisbury eateries to clean the clothes they were wearing at the time. Traces of the nerve agent were reportedly found on and around the table where the pair ate at the Zizzi restaurant.
March 12: Theresa May sets out official findings to parliament that Mr Skripal and his daughter were poisoned with a Novichok: a military grade nerve agent developed by Russia. She gives the Kremlin a deadline of midnight on Tuesday to provide credible answers to British demands.
March 13: After days of silence Donald Trump tells Theresa May that Washington is with Britain "all the way" as London rallies international backing to censure Russia. Moscow accuses Britain of issuing "groundless ultimatums".
March 14: The deadline expires and Mrs May announces a range of measures, including expulsion of Russian diplomats and preparations of new sanctions. A meeting of the UN Security Council is called to discuss the attack.
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Read more:
[ British government urged to expel Russians over poisoning of former spy ]
[ Salisbury: the medieval city at the centre of spy assassination bid ]
[ Lessons not learned after my husband's death, warns Marina Litvinenko ]
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