The widow of murdered former KGB spy Alexander Litvinenko has won a High Court victory raising her hopes of at last obtaining a public inquiry into her husband's death.
Marina Litvinenko challenged the Government's decision last July to refuse an immediate inquiry and instead "wait and see" what a normal inquest could uncover.
Now three High Court judges have ruled that the reasons Home Secretary Theresa May gave for her refusal are so deficient that she must reconsider.
The ruling is significant because the inquest coroner himself - High Court judge Sir Robert Owen - requested a public inquiry and has said there is prima facie evidence that the Russian State could be involved.
His inquest will not be able to consider classified evidence.
Lord Justice Richards, sitting with Lord Justice Treacy and Mr Justice Mitting, said today: "The case for setting up an immediate statutory inquiry as requested by the coroner is plainly a strong one."
But the judge made it clear that the court was stopping short of saying the Government had "no rational option" but to set up the inquiry.
The judges gave the Government until Friday to decide whether to lodge an appeal against their ruling.
Later Mrs Litvinenko, who had appealed to the public for funds to continue her legal battle, said: "I am delighted with today's decision.
"It is a real milestone in my fight to get to the truth behind my husband's murder. We have always said that the reasons that the Government gave for preventing a full inquiry into the involvement of the Russian State didn't make sense. Now the High Court has agreed with us."
She called on Mrs May to "accept this decision".
Mrs Litvinenko says she wants to learn how her 43-year-old husband came to die in 2006 after fleeing Russia and receiving political asylum in the UK.
He was poisoned with radioactive polonium-210 while drinking tea with two Russian men, one a former KGB officer, at the Millennium Hotel in London's Grosvenor Square.
His family believes he was working for MI6 at the time and was killed on the orders of the Kremlin.
Ben Emmerson QC, who represented Mrs Litvinenko, accused Mrs May at the hearing which led to today's ruling of adopting the "bizarre" position of waiting to see what comes out of a pending inquest so restricted that it will not be able to examine secret evidence linked to allegations of Russian state involvement in the death.
Mr Emmerson argued there was "a strong and overwhelming" need for a public inquiry.
He said it was needed to establish whether Mr Litvinenko was the victim of a crime committed "for private criminal purposes" or whether it was a "state-sponsored assassination carried out on the territory of the UK on the orders of the Russian government".
He added that a statutory inquiry was the only way of investigating that central question as it involved accessing "sensitive" information covered by public interest immunity certificates. The courts had decided that information could not be made available to the inquest.