Alamuddin said: "At this stage the ICC case is not about whether Mr Gaddafi and Mr Senussi are guilty of committing crimes against humanity; it is about where their trial should be held.
"In Libya, where they will face a show trial and then be executed, or before an international court in The Hague? No one is arguing that there should be no trial. But we are arguing that there should be justice."
In 1999, Senussi was tried in absentia in France and sentenced to life imprisonment for the shooting down of a UTA airliner over Niger a decade earlier.
United Nations rules stated that the ICC must stage the trial unless Libya could prove it was "willing and able genuinely" to carry out a fair hearing.
Last October, The Hague ruled that Senussi could be tried in Libya, despite claims that he had been mistreated after being extradited from Mauritania, where he had fled after Gaddafi's downfall.
It overlooked the refusal by Libyan authorities to let Alamuddin or any of the legal defence team appointed by the ICC visit Senussi in prison to discuss his case.
Alamuddin was hired for the case by Ben Emmerson QC, the UN special rapporteur on counter-terrorism and human rights, for whom she worked as counsel when he was investigating the use of drones.
The pair also worked together to defend Julian Assange, the founder of WikiLeaks, in extradition proceedings following an application from Sweden.
Emmerson criticised the ICC ruling and said the Libyan justice system was "incapable of conducting fair trials of any Gaddafi-era officials".
Alamuddin, 36, told the Observer newspaper that the "point of the ICC is to be there when national systems can't do the job. Instead, it is giving a flawed, dangerous process the stamp of approval".
The barrister, who is based at London's Doughty Street Chambers, sought out Senussi's daughter, Anoud, after failing to get a visa for Libya. She had been kidnapped and jailed in Tripoli after visiting her father in prison but escaped and fled to London.
Having waited six months for the ICC judges to give a date for the appeal, Alamuddin remains concerned that she cannot gain access to the detail needed to argue her client's case properly.
Legal proceedings began last month with Senussi, looking ill and emaciated, appearing alongside numerous other defendants in a steel cage at the al-Hadba prison, where the trial is being held.
He claimed Libya had broken its promise to the ICC to find him a lawyer.
Prosecutors have refused to let him see the evidence against him, even though he could face the death penalty.
