A suspect in the killing of Alexander Litvinenko will have his last chance to give evidence to the inquiry into the spy's death today.
Dmitri Kovtun had been due to provide testimony by video link from Moscow yesterday but doubts over his position surfaced at the 11th hour.
Chairman Sir Robert Owen gave him a final deadline of 9am today.
Referring to the details of the latest developments outlined by Robin Tam QC, counsel to the inquiry, Sir Robert said yesterday: "The facts as you have outlined them give rise in my mind to the gravest suspicion that an attempt is being made to manipulate the situation so as to enable him hereafter to assert that he would have been willing to give evidence to assist me in this Inquiry, but has been unable to do so for reasons beyond his control."
Three days were set aside for Kovtun's evidence but it emerged last week that he fears he may be committing an offence under Russian law if he gives evidence.
The inquiry was told that Kovtun believes he is bound by a non-disclosure agreement relating to an investigation in Russia.
Mr Litvinenko, 43, died nearly three weeks after drinking tea laced with polonium-210 in London in November 2006.
Police concluded that the fatal dose was probably consumed during a meeting with Kovtun and Andrei Lugovoi at a hotel in central London. British authorities later decided that Lugovoi and Kovtun should be prosecuted for murder.
However, attempts to extradite the pair - who deny involvement - have failed and they remain in Russia.
Both originally refused to take part in the probe, which is sitting at the Royal Courts of Justice in London, before Kovtun dramatically changed his mind.
On his deathbed, Mr Litvinenko accused Russian president Vladimir Putin of ordering his assassination - which the Kremlin denies.