A public inquiry into the death of spy Alexander Litvinenko - who was poisoned with radioactive polonium-210 - will be formally opened today.
The current inquest into the Russian spy's death will be suspended by coroner Sir Robert Owen before the inquiry is opened.
The 43-year-old fled to Britain in 2000 and was poisoned six years later while drinking tea with two Russian men, one a former KGB officer, at the Millennium Hotel in London's Grosvenor Square.
Mr Litvinenko's family believes he was working for MI6 at the time he was killed on the orders of the Kremlin.
Home Secretary Theresa May announced the inquiry last week after the Government had previously insisted it would "wait and see" what a judge-led inquest found.
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The move comes amid a motion of no confidence that was tabled against Labour leader Jeremy Corbyn.
Since Friday's EU result, the Liberal Democrats have recorded thousands of voters signing up to become members.