Home Secretary Theresa May has admitted "international relations" were a factor in the Government's decision not to hold a public inquiry into the death of poisoned spy Alexander Litvinenko.
Coroner Sir Robert Owen had requested that the Government order the inquiry because he could not consider vital secret evidence as part of a normal inquest. This was backed by Mr Litvinenko's widow Marina, who said she and her legal team were "shocked and disappointed" by the Government's refusal.
A letter from Mrs May to Sir Robert explaining the reasons for the decision has now been published. It says: "It is true that international relations have been a factor in the Government's decision-making.
"An inquest managed and run by an independent coroner is more readily explainable to some of our foreign partners, and the integrity of the process more readily grasped, than an inquiry, established by the Government, under a chairman appointed by the Government, which has the power to see Government material potentially relevant to their interests, in secret.
"However this has not been a decisive factor and it if had stood alone would not have led the Government to refuse an inquiry."
Mrs May said that the Government is anxious that Mr Litvinenko's death is properly investigated, and accepts that there are "important factors" in favour of establishing an inquiry.
She wrote: "May I begin by assuring you that the Government shares your concern to make certain that the tragic death of Mr Litvinenko is properly investigated. Like you, the Government is anxious that as much as possible of the investigation is conducted in public, and in such a way that Mr Litvinenko's family are as closely involved in the process as is consistent with the public interest."
Mr Litvinenko, 43, was poisoned with radioactive polonium-210 while drinking tea at the Millennium Hotel in London's Grosvenor Square in 2006. Since his death his widow and son Anatoly have battled to discover the truth about what led to his killing.
Mrs May told Sir Robert the inquest will be able to address key concerns. "It is the view of the Government that, despite the serious concerns you express, an inquest will go a substantial way to addressing or allaying public concern about this incident," she said.
Mrs Litvinenko's solicitor Elena Tsirlina confirmed that they will ask for a judicial review of the decision. She said: "We are in the process of preparing a judicial review claim against the decision by the Secretary of State for the Home Department to decline to cause a public inquiry to be held. We stated our intention at the last pre-inquest hearing. In doing so we have to comply with a number of procedural obligations including securing public funding."