It was a three-year-long process which eventually saw the acquittal of the sociology professor after a second retrial.

Ibrahim was sentenced to seven years in jail twice before a third court acquitted him of all charges.

Founder of the Ibn Khaldoun Centre, Ibrahim was cleared of charges which also included illegally accepting and misusing European Commission Funds.

"It is a day of joy for me and my researchers and friends. It carries a lot of symbols," 64-year-old Ibrahim said.

"It is the third anniversary of my arrest and the closure of the centre. It signifies the triumph of the values for which we have worked for years and for which I went to prison – values of civil society, of democracy, of tolerance and determination to make these values spread," he said.

Ibrahim added that the centre’s work would initially focus on promoting peace in the region, democracy, and development.

Human rights organisations have accused the Egyptian government of using the Ibrahim case to intimidate civil society.

Secretary-General of the independent Egyptian Organisation for Human Rights, said: “The fact that the Ibn Khaldoun Centre has reopened shows that nobody can close down civil society.”

But Egypt denies the accusations and defends the independence of its judiciary.

Ibrahim was sentenced to seven years in jail twice before a third court acquitted him of all charges.

His case gained the attention of Western politicians and human right groups after he was jailed in Cairo's notorious Tora Prison in June 2000 along with 27 supporters.

He was freed in February 2002 when a court ordered a retrial, before going back to prison last July.

But after the US threatened to withhold a $130 million aide package, intended to help compensate Egypt for revenue loss from tourism after the 11 September attacks, Egyptian President Hosni Mubarak ordered a review of his case.