Attorney General Dominic Grieve said today it would be “inappropriate” for him to review the decision to prosecute an SAS sergeant for illegal possession of a weapon.
Defence Secretary Philip Hammond wrote to Mr Grieve today, asking him to review if proper consideration was given to the question of whether a prosecution of Sgt Danny Nightingale was in the public interest before the case was brought to court martial.
But a spokesman for the Attorney General's office responded in a statement: "It would be inappropriate for the Attorney General to review either the decision to prosecute or comment on the appropriateness of the sentence.
"That is a matter for the Court Martial Appeal Court, in due course."
Mr Grieve's response will come as a blow to the family of Sgt Nightingale, who had welcomed Mr Hammond's intervention earlier today.
Speaking before the Attorney General's statement, the soldier's wife Sally said the Defence Secretary's action had given her hope that her husband would be released in time for Christmas.
Sgt Nightingale, a father of two who served in Iraq and Afghanistan, is serving an 18-month sentence at the Military Corrective Training Centre in Colchester, Essex, after admitting possessing a prohibited firearm and ammunition.
He pleaded guilty at court martial to illegally possessing a 9mm Glock pistol which had been packed up and returned to him by colleagues after he had to leave Iraq in a hurry to help organise the funeral of two friends killed in action. He also admitted possessing ammunition.
The court martial heard that the gun was a gift from Iraqi soldiers he had been helping to train, but Sgt Nightingale, who had suffered medical problems affecting his memory, said he did not remember having it.
His lawyers plan to lodge an appeal against his conviction and sentence later this week, as well as applying for bail.
MPs will get an opportunity to raise concerns about his case with Solicitor General Oliver Heald this afternoon, after Canterbury MP Julian Brazier secured a debate in the House of Commons.
Although the MoD is unable to intervene directly in the legal case, it is understood that Mr Hammond's personal view is that it is in the public interest for any appeal to be heard as a matter of urgency.
Announcing Mr Hammond's intervention earlier today, a Ministry of Defence spokesman said: "The Defence Secretary has this morning asked the Attorney General for advice in relation to the case of Sgt Danny Nightingale.
"He has written to the Attorney General asking him to review whether the public interest test has been applied appropriately in this case."
Speaking before the statement by Mr Grieve's office, Mrs Nightingale said that she had been told Mr Hammond's request was "unprecedented".
"It has given me real hope that Danny's case will be urgently reviewed and that he may be home to his family before Christmas," she said.
Sgt Nightingale's solicitor Simon McKay said: "The Attorney General has supervisory responsibilities for the Service Prosecuting Authority that brought the case, and in theory the Attorney General could direct that the appeal is unopposed and/or whether there ought to be a retrial if the convictions are quashed."
The controversial case has sparked outrage from SAS veterans, and four special forces veterans, including the former commanding officer of the SAS, have written an open letter to Prime Minister David Cameron, claiming Sgt Nightingale was "the victim of a monstrous miscarriage of justice".
The soldier's father, Humphrey Nightingale, said today that his son pleaded guilty in the expectation that he would be dealt with leniently.
Mr Nightingale told Sky News: "We knew Danny was not guilty but the judge made it quite clear that if he did not plead guilty, he would be sent to a civilian jail for a minimum of five years.
"Our hands were tied and we had no other option - Danny has a lovely wife and a young family.
"We expected a lenient sentence - maybe suspended - but instead he was sentenced to 18 months."
Mr McKay said that although the Attorney General declined to intervene, he was glad it had been brought to his attention.
"The next stage has to be to get the appeal in and see what the Service Prosecuting Authority, which is under his umbrella, has to say about it," he said.
He said that, at the moment, the Attorney General would find it hard to review the situation, as he does not know any details about the appeal that they plan to lodge later this week.
"He would need to see that, then reach a view as to how the matter is conducted thereafter," he said.
Mr McKay said they remain confident of the prospect of an appeal, adding: "I am working with William Clegg QC, one of the most experienced criminal silks in the country, and there is a strong degree of confidence."
Lieutenant Colonel Richard Williams, who was Sgt Nightingale's commanding officer in Iraq, said concerns about an "injustice" appeared to be being taken seriously by the Government.
Asked if he was disappointed with Mr Grieve's intervention, he told BBC Radio 4's The World At One: "Yes, and I'm not fully cognisant of how it sits constitutionally as we call it.
"But the fact that the Secretary of State has taken such an interest and asked the Attorney General to take such an interest indicates that what we are feeling, that there has been an injustice, is being taken seriously."