- 12th October 2004 Yasser Arafat falls ill at his compound. He is flown to a French military hospital for treatment
- 11th November 2004 He passes away at the age of 75
- September 2005 The New York Times obtains a copy of his medical records which shows that he died as a result of a stroke caused by an unknown infection
- July 2012 An investigation by Al Jazeera reveals high traces of the poison polonium in his personal possessions
- August 2012 French prosecutors launch an investigation after Swiss scientists find traces of radioactive polonium-210 in Yasser Arafat's belongings
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
A man, apparently armed with a small axe and a large stick, was detained close to the event and police cleared the area as a precaution.