The inquest into the death of former Russian spy Alexander Litvinenko will take place early next year.
Mr Litvinenko, 43, is thought to have been poisoned with polonium-210 after having tea with two Russians at a central London hotel in November 2006.
Sir Robert Owen, assistant deputy coroner, apologised for the delay and said it would take place in early 2013.
The prime suspect, Andrei Lugovoi, has since been elected as a Russian MP and cannot be extradited to the UK.
Alex Goldfarb, an author and friend of Mr Litvinenko, told the hearing: "We think this was a political murder perpetrated by the Russian state."
The BBC's security correspondent Gordon Corera tweeted: "Sir Robert (says) six-year gap between Alexander Litvinenko's death and inquest was to be regretted. 'There will be no further delay'."
Counsel to the inquest, Hugo Davies, said some foreign witnesses could give evidence by video link.
He said all competing theories would be examined, adding: "The court is committed to transparency."
The hearing was told "interested parties" would receive a summary of Scotland Yard's investigation report into Mr Litvinenko's death but certain intelligence reports would be redacted.
The Metropolitan Police were also asked to look at any links between Mr Litvinenko and British intelligence. That section will be redacted from the report given to interested parties but Mr Davies said this should not be taken as confirming any links.
Mr Lugovoi is currently represented as an interested person at the inquest but Dimitri Kovtun, another Russian former agent who was present at a crucial meeting with Mr Litvinenko on 1 November 2006, is not represented.
An inquest into Alexander Litvinenko's death was opened just weeks after he died but then immediately adjourned while a police investigation got under way.
That investigation led to the Crown Prosecution Service announcing it wanted Andrei Lugovoi extradited to stand trial.
But nearly six years after Mr Litvinenko's death and with no sign of a trial, Mr Litvinenko's family and friends have lost patience and pushed to re-open the inquest to try to provide some answers.
A key question is how broadly the inquest will range.
If it tries to answer not just how he died but why, and look at issues of where the radioactive polonium might have come from, then it may well lead to renewed diplomatic tensions with Moscow.
Relations had only just recovered from the original investigation in the wake of which both sides had expelled diplomats.
Our correspondent says others with interested person status include the widow and son of Mr Litvinenko, and Russian tycoon Boris Berezvosky.
It is understood the Home Secretary, Theresa May, has also become an "interested party".
A website has been launched for the inquest, which contains details about the legal process and short biographies about the lawyers involved - it will be updated during the inquest.
Earlier Mr Litvinenko's widow Marina told the BBC she hoped the inquest would establish the truth about what happened to him.
Mrs Litvinenko said: "I would like to know who killed him and why. I said this six years ago and I hope I will know this finally."
The death of Mr Litvinenko, a former Russian security officer who had obtained asylum in Britain, led to a major diplomatic incident as the Kremlin was accused of masterminding his murder.
British prosecutors named Mr Lugovoi as the main suspect but he was later elected as a Russian MP and Moscow refused to send him to the UK for questioning. He has denied involvement.
Prime Minister David Cameron raised the issue with Russian President Vladimir Putin recently during his visit to London.
Earlier this year the then Justice Secretary, Ken Clarke, wrote to the then coroner asking for clarification about the estimated £4m inquest costs.