Despite a Bulgarian government minister admitting that "doubt exists" responsibility to act was passed to Westminster.

Michael's solicitor John Weate said: "Once it became clear that the Bulgarian authorities were unwilling to act to re-open the case or pardon Michael, Jack Straw was asked to grant a UK pardon pursuant to the Royal Prerogative of Mercy.

"Jack Straw has paid close personal attention to this case, and he has indicated that he has spent more time on this matter than on any other individual case since becoming minister.

"On a recent BBC documentary Mr Straw indicated that he was seeking legal advice as to whether he had jurisdiction to act in this case.

"But in July Mr Straw personally indicated that the advice he had received was that he did not have the power to pardon a repatriated prisoner on the grounds of a miscarriage of justice, because of Article 13 of the 1983 Convention, and the Repatriation of Prisoners Act 1984 (RPA).

"It is this decision that is being challenged by the application for judicial review.

"The power to pardon is pursuant to the Royal Prerogative of Mercy.

"It is a broad constitutional safeguard, exercised by the relevant minister of state, to release a prisoner from his punishment.

"It can be exercised for a number of reasons, including where there has been a wrongful conviction which cannot be dealt with by the normal judicial process.

"This form of the pardon is rare because of the ability of the Criminal Cases Review Commission and the Court of Appeal to investigate alleged miscarriages of justice and correct them.

"However the power exists, and for more than a century the policy has been to pardon where the Secretary of State believes the prisoner to be 'morally and technically innocent', and there is no other practical way of dealing with the case.

"The application for judicial review will argue that Article 12 of the Convention expressly acknowledges that both states have the power to pardon a repatriated prisoner in accordance with their domestic law.

"We will argue there is nothing in law which precludes the operation of a pardon in such cases.

"The judicial review application will be lodged with an application for expedition in light of the fact that Michael has already served more than 3 years of his sentence."

Liverpool Riverside MP Louise Ellman said: "This application for judicial review is a vital step in securing justice for Michael Shields.

"It's essential that there is legal clarity about who has jurisdiction over Michael's future."

Liverpool City Council opposition Labour group leader Joe Anderson Said: "It's a disgrace when we have to pursue a judicial review against our own Government.

"They know Michael Shields is totally innocent yet they do nothing.

"Their feeble excuses mean Michael has spent three years in jail for a crime that others committed.

"I'm ashamed of this Government’s cowardice in not taking action to free a man they know to be innocent."

Michael's father, window cleaner Michael Shields snr said: "I am saddened that we have had to go through this process and hope that the Court will confirm that Mr. Straw can make a decision on the merits of Michael’s Case as soon as possible.

"I just want my son home to be with his family."