Egyptian cleric Osama Hassan Mustafa Nasr, known as Abu Omar. AP Photo/Nasser Nasser

A former CIA operative is to be the first to be extradited to face court over the Bush administration's heavily criticised policy of kidnapping terror suspects and smuggling them to third countries for interrogation.

In the latest twist in a decades-long transatlantic espionage scandal, the Portuguese Supreme Court has upheld a request from Italy to extradite Sabrina de Sousa, who was detained in Lisbon last year.

Ms de Sousa, 57, has already been convicted in absentia for her alleged role in the CIA kidnapping of Abu Omar, a Muslim cleric accused of jihadist sympathies. He was seized in broad daylight from a Milan street, flown to Egypt and handed over to the authorities there who are said to have jailed and tortured him for four years before releasing him without charge.

The development sets the stage for a high-profile trial in Italy that could reveal new details about the CIA’s secret transfer and detention of terror suspects between countries in Europe under the so-called extraordinary rendition programme that operated for years after the 9/11 attacks.

“This gives me the chance to finally clear my name after a decade of legal jeopardy that made it nearly impossible to expose a cover up,” Ms de Sousa told the Telegraph from Lisbon.

Under the terms of the extradition, she will be allowed to appeal against her conviction and four-year sentence, bringing her side of the story into the open.

“If this ruling truly guarantees me the right to a fair trial in Italy, then I’m ready,” she said.

Unlike other countries who co-operated in the rendition programme, Italy investigated its own practices and put individuals on trial as a result - including both American agents and members of its own security services.

Ms de Sousa was among 26 Americans convicted in absentia in 2009 for the kidnapping of Abu Omar, whose real name is Osama Moustafa Hassan Nasr.

He was seized by US and Italian agents in 2003, and transferred to Egypt via US air bases in Italy and Germany.

Ms de Sousa was one of several CIA agents working undercover in Milan as accredited diplomats, but maintains she was not responsible for planning, authorizing or executing the rendition.

She said the decision was taken by Jeffrey Castelli, a former Rome CIA station chief who was one of three CIA officers whose claims to diplomatic immunity were accepted.

Other senior American operatives and military officials who were among those convicted were subsequently pardoned, following high-level diplomatic negotiations involving the Italian authorities on the one side and the Pentagon, the then US secretary of state, Hillary Clinton, and attorney-general, Eric Holder. The Italian agents were acquitted, granted immunity or offered plea bargains.

Hillary Clinton was acquitted of her role in the kidnapping following high-level negotiations. REUTERS/Jim Young

However, Ms de Sousa left the CIA in 2009 and was excluded from both immunity and pardon deals. A dual US-Portuguese national, she was arrested under a European warrant after moving to Portugal last year.

She has since been under state arrest, her passports confiscated, while Portugal’s courts considered extradition.

She has now begun speaking out against both the rendition programme and the American government’s reaction to the Italian case.

“One man’s decision destroyed so many lives, including that of Abu Omar, and yet the CIA is hell bent on protecting him,” she said, of the immunity granted to Mr Castelli.

“This case is no longer just about me. It is symbolic of the CIA’s defiant refusal to hold accountable those who authorise every rendition, detention and interrogation programme worldwide."

Ms de Sousa’s lawyers point out the contradiction in the fact that some officers have been granted full or partial pardons but not Ms de Sousa. However, they are hindered by the fact that the US government has refused to confirm its involvement in Abu Omar’s rendition .

In declarations filed in the US courts by the CIA last month and seen by the Telegraph, the US government again refused to release key documents on grounds the material was classified and too sensitive.

“The CIA has put her in an impossible position,” said Jeffrey Light, Ms de Sousa's US lawyer. “They have evidence she needs to present a defence, but refuse to process her freedom of information requests.”

The Portuguese lawyer handling the case, Manuel Magalhaes e Silva, said that the extradition ruling meant the Italian courts would allow new evidence to be heard. However, Ms de Sousa's Italian legal team believes the best chance for resolution is ultimately with the presidential office in Rome, given the international issues at stake and the president's role in agreeing the earlier pardons.

The case will once again expose continuing investigations into the rendition programme, in which suspected jihadists were flown secretly around the world for interrogation and imprisonment.

John Brennan, the director of the CIA. Reuters/Jason Reed

In an interview with La Repubblica, a former CIA officer responsible for the programme, Michael Scheuer, described Abu Omar as “low-hanging fruit” who did not meet the rendition threshold.

However, Ms de Sousa said that Mr Castelli still managed to obtain authorisation from Tyler Drumheller, Chief of European Operations, Chief of Counterterrorism Jose Rodriguez, CIA Director of Operations James Pavitt and his deputy at the time.

She said that CIA Chief Counsel John Rizzo and lawyers for the State Department and the National Security Council also signed off.

Earlier this year, the European Court of Human Rights condemned Italy for violating Abu Omar’s human rights, saying it knew about and participated in the CIA’s kidnapping, then failed to offer redress or hold anyone accountable.